[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #20 from rguenther at suse dot de  ---
On Tue, 13 Mar 2018, nickc at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847
> 
> --- Comment #14 from Nick Clifton  ---
> Created attachment 43643
>   --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43643=edit
> Proposed patch
> 
> Hi Guys.
> 
>   Here is a possible patch, although it is a bit hackish.
>   Richard might not like it because it changes gcc/lto-wrapper.c rather than
>   the linker, but I honestly think that the linker is doing the right thing
>   in this case.

Note with all workarounds proposed they have to "work" (aka not break)
with non-GNU ld including gold, Solaris ld, HPUX ld, etc. ...

I presume the linker plugin API doesn't allow us to even tell whether
--gc-sections was specified for the link or not.  So I agree with HJ
that this needs to be fixed in the linker.  Given there's a known
workaround for users that isn't too bad.

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #19 from H.J. Lu  ---
(In reply to rguent...@suse.de from comment #11)

> Nah, just the following - you removed LTO testing of prettyprinters
> 
> Index: libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
> ===
> --- libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp  
> (revision 258481)
> +++ libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp  
> (working copy)
> @@ -50,7 +50,7 @@ gdb-dg-runtest [lsort [glob $srcdir/$sub
>  if { [check_effective_target_lto] } {
>append cxxflags " -flto"
># work around sourceware.org 20882
> -  regsub {^(.*)-Wl,--gc-sections(.*)$} $cxxldflags {\1\2} cxxldflags
> +  #regsub {^(.*)-Wl,--gc-sections(.*)$} $cxxldflags {\1\2} cxxldflags
>gdb-dg-runtest [lsort [glob $srcdir/$subdir/*.cc]] \
>  "" "$DEFAULT_CXXFLAGS -flto $PCH_CXXFLAGS"
>  }

With this patch applied:

https://sourceware.org/ml/binutils/2018-03/msg00175.html

I got

# of expected passes140

=== libstdc++ Summary ===

# of expected passes201

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #18 from rguenther at suse dot de  ---
On March 13, 2018 5:15:33 PM GMT+01:00, "nickc at gcc dot gnu.org"
 wrote:
>https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847
>
>--- Comment #16 from Nick Clifton  ---
>Hi H.J.
>
>(In reply to H.J. Lu from comment #15)
>> It should be fixed in linker.
>
>OK - so how does the linker distinguish between a file that only
>contains
>debug information, none of which is needed, and a file that only
>contains
>debug information of which some/all actually is needed ?

There are used symbols and associated debug sections need to be kept. If
nothing references the debug it can be discarded. 

>Cheers
>  Nick

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

H.J. Lu  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 Resolution|--- |MOVED

--- Comment #17 from H.J. Lu  ---
Moved to

https://sourceware.org/bugzilla/show_bug.cgi?id=20882

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[nickc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #16 from Nick Clifton  ---
Hi H.J.

(In reply to H.J. Lu from comment #15)
> It should be fixed in linker.

OK - so how does the linker distinguish between a file that only contains
debug information, none of which is needed, and a file that only contains
debug information of which some/all actually is needed ?

Cheers
  Nick

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #15 from H.J. Lu  ---
(In reply to Nick Clifton from comment #14)
> Created attachment 43643 [details]
> Proposed patch
> 
> Hi Guys.
> 
>   Here is a possible patch, although it is a bit hackish.
>   Richard might not like it because it changes gcc/lto-wrapper.c rather than
>   the linker, but I honestly think that the linker is doing the right thing
>   in this case.
> 

It should be fixed in linker.

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[nickc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #14 from Nick Clifton  ---
Created attachment 43643
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43643=edit
Proposed patch

Hi Guys.

  Here is a possible patch, although it is a bit hackish.
  Richard might not like it because it changes gcc/lto-wrapper.c rather than
  the linker, but I honestly think that the linker is doing the right thing
  in this case.

Cheers
  Nick

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #13 from David Malcolm  ---
(In reply to H.J. Lu from comment #12)
> Need GCC 8 to reproduce:
Thanks.  What version of ld was this with?

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

H.J. Lu  changed:

   What|Removed |Added

 Status|WAITING |NEW

--- Comment #12 from H.J. Lu  ---
Need GCC 8 to reproduce:

/usr/gcc-8.0.1-x32/bin/gcc -I ./src -flto -O2 -g -c src/bootchart.c -o
build/bootchart.o
/usr/gcc-8.0.1-x32/bin/gcc -I ./src -flto -O2 -g -c src/log.c -o build/log.o
/usr/gcc-8.0.1-x32/bin/gcc -flto -g -Wl,--gc-sections -Wl,--print-gc-sections \
  build/bootchart.o build/log.o \
  -o build/systemd-bootchart
/usr/local/bin/ld: removing unused section '.rodata.cst4' in file
'/lib/../lib64/crt1.o'
/usr/local/bin/ld: removing unused section '.data' in file
'/lib/../lib64/crt1.o'
/usr/local/bin/ld: removing unused section '.data' in file
'/usr/gcc-8.0.1-x32/lib/gcc/x86_64-pc-linux-gnu/8.0.1/crtbegin.o'
/usr/local/bin/ld: removing unused section '.debug_abbrev' in file
'/tmp/ccpV3zjtdebugobj'
/usr/local/bin/ld: removing unused section '.debug_str' in file
'/tmp/ccpV3zjtdebugobj'
/usr/lib/rpm/debugedit build/systemd-bootchart
/usr/lib/rpm/debugedit: build/systemd-bootchart: Invalid .line_table offset
0x2b0803
make: *** [Makefile:23: test] Segmentation fault

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #11 from rguenther at suse dot de  ---
On Tue, 13 Mar 2018, hjl.tools at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847
> 
> --- Comment #9 from H.J. Lu  ---
> (In reply to rguent...@suse.de from comment #6)
> > 
> > make check-target-libstdc++-v3 RUNTESTFLAGS="prettyprinters.exp"
> 
> I tried:
> 
> diff --git 
> a/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
> b/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
> index c51b1ffb21c..fab6ef11947 100644
> --- a/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
> +++ b/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
> @@ -47,14 +47,6 @@ global PCH_CXXFLAGS
>  gdb-dg-runtest [lsort [glob $srcdir/$subdir/*.cc]] \
>"" "$DEFAULT_CXXFLAGS $PCH_CXXFLAGS"
> 
> -if { [check_effective_target_lto] } {
> -  append cxxflags " -flto"
> -  # work around sourceware.org 20882
> -  regsub {^(.*)-Wl,--gc-sections(.*)$} $cxxldflags {\1\2} cxxldflags
> -  gdb-dg-runtest [lsort [glob $srcdir/$subdir/*.cc]] \
> -"" "$DEFAULT_CXXFLAGS -flto $PCH_CXXFLAGS"
> -}
> -
>  if [info exists guality_gdb_name] {
>  unsetenv GUALITY_GDB_NAME
>  }

Nah, just the following - you removed LTO testing of prettyprinters

Index: libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
===
--- libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp  
(revision 258481)
+++ libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp  
(working copy)
@@ -50,7 +50,7 @@ gdb-dg-runtest [lsort [glob $srcdir/$sub
 if { [check_effective_target_lto] } {
   append cxxflags " -flto"
   # work around sourceware.org 20882
-  regsub {^(.*)-Wl,--gc-sections(.*)$} $cxxldflags {\1\2} cxxldflags
+  #regsub {^(.*)-Wl,--gc-sections(.*)$} $cxxldflags {\1\2} cxxldflags
   gdb-dg-runtest [lsort [glob $srcdir/$subdir/*.cc]] \
 "" "$DEFAULT_CXXFLAGS -flto $PCH_CXXFLAGS"
 }

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #10 from H.J. Lu  ---
(In reply to rguent...@suse.de from comment #8)
> On Tue, 13 Mar 2018, hjl.tools at gmail dot com wrote:
> 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847
> > 
> > --- Comment #7 from H.J. Lu  ---
> > Binutils 2.30 branch looks normal:
> 
> I tried 2.30 branch at 4cd0043413 and that still has UNRESOLVED
> libstdc++ prettyprinter tests.

binutils-2_30-branch at commit ff7e1a287ace9c also works for me.
Please show me the relevant libstdc++.log.

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #9 from H.J. Lu  ---
(In reply to rguent...@suse.de from comment #6)
> 
> make check-target-libstdc++-v3 RUNTESTFLAGS="prettyprinters.exp"

I tried:

diff --git a/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
b/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
index c51b1ffb21c..fab6ef11947 100644
--- a/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
+++ b/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp
@@ -47,14 +47,6 @@ global PCH_CXXFLAGS
 gdb-dg-runtest [lsort [glob $srcdir/$subdir/*.cc]] \
   "" "$DEFAULT_CXXFLAGS $PCH_CXXFLAGS"

-if { [check_effective_target_lto] } {
-  append cxxflags " -flto"
-  # work around sourceware.org 20882
-  regsub {^(.*)-Wl,--gc-sections(.*)$} $cxxldflags {\1\2} cxxldflags
-  gdb-dg-runtest [lsort [glob $srcdir/$subdir/*.cc]] \
-"" "$DEFAULT_CXXFLAGS -flto $PCH_CXXFLAGS"
-}
-
 if [info exists guality_gdb_name] {
 unsetenv GUALITY_GDB_NAME
 }

> with binutils master and the prettyprinters.exp hack removed?

=== libstdc++ Summary ===

# of expected passes140

> Do you know what fixed it on master?

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b7c871edcd83ccdc5fcd8148a7f433efd6b52255

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #8 from rguenther at suse dot de  ---
On Tue, 13 Mar 2018, hjl.tools at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847
> 
> --- Comment #7 from H.J. Lu  ---
> Binutils 2.30 branch looks normal:

I tried 2.30 branch at 4cd0043413 and that still has UNRESOLVED
libstdc++ prettyprinter tests.

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #7 from H.J. Lu  ---
Binutils 2.30 branch looks normal:

[hjl@gnu-cfl-1 rhbz-1543912]$ gcc -flto -g -Wl,--gc-sections
-Wl,--print-gc-sections   build/bootchart.o build/log.o   -o
build/systemd-bootchart -B./ -Wl,-v
collect2 version 7.3.1 20180303 (Red Hat 7.3.1-5)
./ld -plugin /usr/libexec/gcc/x86_64-redhat-linux/7/liblto_plugin.so
-plugin-opt=/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper
-plugin-opt=-fresolution=/tmp/cc1PZVqG.res -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s --build-id
--no-add-needed --eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker
/lib64/ld-linux-x86-64.so.2 -o build/systemd-bootchart
/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crt1.o
/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o -L.
-L/usr/lib/gcc/x86_64-redhat-linux/7
-L/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64 -L/lib/../lib64
-L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/7/../../.. --gc-sections
--print-gc-sections build/bootchart.o build/log.o -v -lgcc --as-needed -lgcc_s
--no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/x86_64-redhat-linux/7/crtend.o
/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crtn.o
GNU ld (GNU Binutils) 2.30.0.20180313
./ld: Removing unused section '.rodata.cst4' in file
'/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crt1.o'
./ld: Removing unused section '.data' in file
'/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crt1.o'
./ld: Removing unused section '.rodata' in file
'/usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o'
[hjl@gnu-cfl-1 rhbz-1543912]$ 

Please try FSF binutils 2.30, not from Fedora 28.

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #6 from rguenther at suse dot de  ---
On Tue, 13 Mar 2018, hjl.tools at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847
> 
> --- Comment #5 from H.J. Lu  ---
> (In reply to David Malcolm from comment #0)
> > The downstream bug report:
> >   https://bugzilla.redhat.com/show_bug.cgi?id=1543912
> > describes a problem building systemd and systemd-bootchart with gcc 8, which
> > turned out to be due to those packages' configure scripts injecting both
> >   -flto
> > and
> >   -Wl,--gc-sections
> > 
> > They build fine with just one of them, but with both, the binaries have
> > corrupt DWARF debuginfo.
> > 
> > Adding "-Wl,--print-gc-sections" shows the issue more clearly.
> > 
> > I created a minimal reproducer here:
> >   https://github.com/davidmalcolm/rhbz-1543912
> > with which I can reproduce the issue, using:
> >   gcc-8.0.1-0.16.fc29.x86_64
> >   binutils-2.30-6.fc29.x86_64
> > (this is on Fedora in a chroot via "mock -r fedora-rawhide-x86_64 shell";
> > I'm still working on reproducing this outside a chroot)
> > 
> > $ make
> > gcc -I ./src -flto -O2 -g -c src/bootchart.c -o build/bootchart.o
> > gcc -I ./src -flto -O2 -g -c src/log.c -o build/log.o
> > gcc -flto -g -Wl,--gc-sections -Wl,--print-gc-sections \
> >   build/bootchart.o build/log.o \
> >   -o build/systemd-bootchart
> > /usr/bin/ld: Removing unused section '.rodata.cst4' in file
> > '/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crt1.o'
> > /usr/bin/ld: Removing unused section '.data' in file
> > '/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crt1.o'
> > /usr/bin/ld: Removing unused section '.rodata' in file
> > '/usr/lib/gcc/x86_64-redhat-linux/8/crtbegin.o'
> > /usr/bin/ld: Removing unused section '.debug_abbrev' in file
> > '/tmp/cc1vnNPxdebugobj'
> > /usr/bin/ld: Removing unused section '.debug_str' in file
> > '/tmp/cc1vnNPxdebugobj'
> > /usr/lib/rpm/debugedit build/systemd-bootchart
> > /usr/lib/rpm/debugedit: build/systemd-bootchart: Invalid .line_table offset
> > 0x2b0803
> > /usr/lib/rpm/debugedit: build/systemd-bootchart: Could not find DWARF
> > abbreviation 7
> > 
> 
> With binutils master branch, I got
> 
> mkdir build
> gcc -I ./src -flto -O2 -g -c src/bootchart.c -o build/bootchart.o
> gcc -I ./src -flto -O2 -g -c src/log.c -o build/log.o
> gcc -flto -g -Wl,--gc-sections -Wl,--print-gc-sections \
>   build/bootchart.o build/log.o \
>   -o build/systemd-bootchart
> /usr/local/bin/ld: removing unused section '.rodata.cst4' in file
> '/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crt1.o'
> /usr/local/bin/ld: removing unused section '.data' in file
> '/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crt1.o'
> /usr/local/bin/ld: removing unused section '.rodata' in file
> '/usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o'
> /usr/lib/rpm/debugedit build/systemd-bootchart
> 
> Does it look OK?

Can you try

make check-target-libstdc++-v3 RUNTESTFLAGS="prettyprinters.exp"

with binutils master and the prettyprinters.exp hack removed?

Do you know what fixed it on master?

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

H.J. Lu  changed:

   What|Removed |Added

 Status|UNCONFIRMED |WAITING
   Last reconfirmed||2018-03-13
 CC||hjl.tools at gmail dot com
 Ever confirmed|0   |1

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #5 from H.J. Lu  ---
(In reply to David Malcolm from comment #0)
> The downstream bug report:
>   https://bugzilla.redhat.com/show_bug.cgi?id=1543912
> describes a problem building systemd and systemd-bootchart with gcc 8, which
> turned out to be due to those packages' configure scripts injecting both
>   -flto
> and
>   -Wl,--gc-sections
> 
> They build fine with just one of them, but with both, the binaries have
> corrupt DWARF debuginfo.
> 
> Adding "-Wl,--print-gc-sections" shows the issue more clearly.
> 
> I created a minimal reproducer here:
>   https://github.com/davidmalcolm/rhbz-1543912
> with which I can reproduce the issue, using:
>   gcc-8.0.1-0.16.fc29.x86_64
>   binutils-2.30-6.fc29.x86_64
> (this is on Fedora in a chroot via "mock -r fedora-rawhide-x86_64 shell";
> I'm still working on reproducing this outside a chroot)
> 
> $ make
> gcc -I ./src -flto -O2 -g -c src/bootchart.c -o build/bootchart.o
> gcc -I ./src -flto -O2 -g -c src/log.c -o build/log.o
> gcc -flto -g -Wl,--gc-sections -Wl,--print-gc-sections \
>   build/bootchart.o build/log.o \
>   -o build/systemd-bootchart
> /usr/bin/ld: Removing unused section '.rodata.cst4' in file
> '/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crt1.o'
> /usr/bin/ld: Removing unused section '.data' in file
> '/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crt1.o'
> /usr/bin/ld: Removing unused section '.rodata' in file
> '/usr/lib/gcc/x86_64-redhat-linux/8/crtbegin.o'
> /usr/bin/ld: Removing unused section '.debug_abbrev' in file
> '/tmp/cc1vnNPxdebugobj'
> /usr/bin/ld: Removing unused section '.debug_str' in file
> '/tmp/cc1vnNPxdebugobj'
> /usr/lib/rpm/debugedit build/systemd-bootchart
> /usr/lib/rpm/debugedit: build/systemd-bootchart: Invalid .line_table offset
> 0x2b0803
> /usr/lib/rpm/debugedit: build/systemd-bootchart: Could not find DWARF
> abbreviation 7
> 

With binutils master branch, I got

mkdir build
gcc -I ./src -flto -O2 -g -c src/bootchart.c -o build/bootchart.o
gcc -I ./src -flto -O2 -g -c src/log.c -o build/log.o
gcc -flto -g -Wl,--gc-sections -Wl,--print-gc-sections \
  build/bootchart.o build/log.o \
  -o build/systemd-bootchart
/usr/local/bin/ld: removing unused section '.rodata.cst4' in file
'/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crt1.o'
/usr/local/bin/ld: removing unused section '.data' in file
'/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crt1.o'
/usr/local/bin/ld: removing unused section '.rodata' in file
'/usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o'
/usr/lib/rpm/debugedit build/systemd-bootchart

Does it look OK?

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #4 from Richard Biener  ---
Note that back in time using gold made things work.

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

Richard Biener  changed:

   What|Removed |Added

   See Also||https://sourceware.org/bugz
   ||illa/show_bug.cgi?id=20882

--- Comment #3 from Richard Biener  ---
I have re-opened the binutils bug.

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

Richard Biener  changed:

   What|Removed |Added

   Keywords||lto
   Target Milestone|--- |8.0

--- Comment #2 from Richard Biener  ---
Note this is clearly a binutils bug, not a GCC one.  Note I think we cannot
work around this ld bug in GCC.

The 20882 workaround cannot be removed from prettyprinters.exp when using
binutils 2.29.1.  I then still get

=== libstdc++ Summary ===

# of expected passes270
# of unsupported tests  14

instead of
=== libstdc++ Summary ===

# of expected passes512

errors are like


Dwarf Error: could not find abbrev number 100 [in module
/tmp/obj/x86_64-pc-linux-gnu/libstdc++-v3/testsuite/48362.exe]^M
skipping: Dwarf Error: could not find abbrev number 100 [in module
/tmp/obj/x86_64-pc-linux-gnu/libstdc++-v3/testsuite/48362.exe]^M
48362.gdb:5: Error in sourced command file:^M
No symbol table is loaded.  Use the "file" command.^M
skipping: 48362.gdb:5: Error in sourced command file:^M
skipping: No symbol table is loaded.  Use the "file" command.^M
UNSUPPORTED: libstdc++-prettyprinters/48362.cc

[Bug lto/84847] [8 Regression] Incompatibility between early LTO debug and "-Wl,--gc-sections" leads to corrupt DWARF debuginfo

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847

--- Comment #1 from rguenther at suse dot de  ---
On Tue, 13 Mar 2018, dmalcolm at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84847
> 
> Bug ID: 84847
>Summary: [8 Regression] Incompatibility between early LTO debug
> and "-Wl,--gc-sections" leads to corrupt DWARF
> debuginfo
>Product: gcc
>Version: 8.0
> Status: UNCONFIRMED
>   Severity: normal
>   Priority: P3
>  Component: lto
>   Assignee: unassigned at gcc dot gnu.org
>   Reporter: dmalcolm at gcc dot gnu.org
> CC: marxin at gcc dot gnu.org, nickc at gcc dot gnu.org,
> rguenth at gcc dot gnu.org
>   Target Milestone: ---
> 
> The downstream bug report:
>   https://bugzilla.redhat.com/show_bug.cgi?id=1543912
> describes a problem building systemd and systemd-bootchart with gcc 8, which
> turned out to be due to those packages' configure scripts injecting both
>   -flto
> and
>   -Wl,--gc-sections
> 
> They build fine with just one of them, but with both, the binaries have 
> corrupt
> DWARF debuginfo.
> 
> Adding "-Wl,--print-gc-sections" shows the issue more clearly.
> 
> I created a minimal reproducer here:
>   https://github.com/davidmalcolm/rhbz-1543912
> with which I can reproduce the issue, using:
>   gcc-8.0.1-0.16.fc29.x86_64
>   binutils-2.30-6.fc29.x86_64
> (this is on Fedora in a chroot via "mock -r fedora-rawhide-x86_64 shell"; I'm
> still working on reproducing this outside a chroot)
> 
> $ make
> gcc -I ./src -flto -O2 -g -c src/bootchart.c -o build/bootchart.o
> gcc -I ./src -flto -O2 -g -c src/log.c -o build/log.o
> gcc -flto -g -Wl,--gc-sections -Wl,--print-gc-sections \
>   build/bootchart.o build/log.o \
>   -o build/systemd-bootchart
> /usr/bin/ld: Removing unused section '.rodata.cst4' in file
> '/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crt1.o'
> /usr/bin/ld: Removing unused section '.data' in file
> '/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crt1.o'
> /usr/bin/ld: Removing unused section '.rodata' in file
> '/usr/lib/gcc/x86_64-redhat-linux/8/crtbegin.o'
> /usr/bin/ld: Removing unused section '.debug_abbrev' in file
> '/tmp/cc1vnNPxdebugobj'
> /usr/bin/ld: Removing unused section '.debug_str' in file
> '/tmp/cc1vnNPxdebugobj'
> /usr/lib/rpm/debugedit build/systemd-bootchart
> /usr/lib/rpm/debugedit: build/systemd-bootchart: Invalid .line_table offset
> 0x2b0803
> /usr/lib/rpm/debugedit: build/systemd-bootchart: Could not find DWARF
> abbreviation 7
> 
> In the above, note how ld has garbage-collected the '.debug_abbrev' and
> '.debug_str' sections from the /tmp/cc*debugobj file.
> 
> Examining the binary via
>   eu-readelf -w build/systemd-bootchart
> shows bogus-looking compile_unit DIEs in the binary:
> 
> DWARF section [23] '.debug_info' at offset 0x10a6:
>  [Offset]
>  Compilation unit at offset 0:
>  Version: 4, Abbreviation section offset: 0, Address size: 8, Offset size: 4
>  [ b]  compile_unit
>producer (strp) "/builddir/build/BUILD/minimizing-2"
>language (data1) C99 (12)
>name (strp) "/builddir/build/BUILD/minimizing-2"
>comp_dir (strp) "/builddir/build/BUILD/minimizing-2"
>ranges   (sec_offset) range list [ 2]
>low_pc   (addr) 0x00250e030100
>  Compilation unit at offset 105:
>  Version: 4, Abbreviation section offset: 0, Address size: 8, Offset size: 4
>  [74]  compile_unit
>producer (strp) "/builddir/build/BUILD/minimizing-2"
>language (data1) C99 (12)
>name (strp) "/builddir/build/BUILD/minimizing-2"
>comp_dir (strp) "/builddir/build/BUILD/minimizing-2"
>ranges   (sec_offset) range list [ 2]
>low_pc   (addr) 0x870006030100
> 
> Note how every string is using string 0.
> 
> Removing the -Wl,--gc-sections leads to sane-looking DIEs.
> 
> The issue seems to be that lto-wrapper generates /tmp/cc*debugobj files
> containing "early LTO debug info", but, quoting Nick in:
>   https://bugzilla.redhat.com/show_bug.cgi?id=1543912#c22
> >   I have now found out what it happening, although I am still a little bit
> >   confused as to why it should be occurring.  The LTO pass is producing an
> >   object file that only contains debug information:
> >
> > /dev/shm/ccqhNEybdebugobj
> >
> >   (There was a clue in the filename, but I did not pay attention to this).
> >
> >   The linker's garbage collection code reasons that any file that does not
> >   have *any* allocatable sections[1] can automatically be discarded, since 
> > it
> >   cannot have any effect on the execution of the resulting binary, right ?
> > ...
> >
> >   So this