Re: [PATCH] i386: Allow -mlarge-data-threshold with -mcmodel=large
On Wed, May 10, 2023 at 2:58 AM Uros Bizjak wrote:
>
> On Fri, Apr 28, 2023 at 2:47 AM Fangrui Song wrote:
> >
> > When using -mcmodel=medium, large data is placed into .l* sections. GNU ld
> > places .l* sections into separate output sections. If small and medium
> > code model object files are mixed, the .l* sections won't cause
> > relocation overflow pressure on sections in -mcmodel=small object files.
> >
> > However, when using -mcmodel=large, -mlarge-data-threshold doesn't apply.
> > This
> > means that the .rodata/.data/.bss sections may cause relocation overflow
> > pressure on sections in -mcmodel=small object files.
> >
> > This patch allows -mcmodel=large to generate .l* sections.
>
> The x86_64 psABI does not specify how -mlarge-threshold is handled
> with -mcmodel=large and it also doesn't mention that -mcmodel=large
> inherits handling from -mcmodel=medium. The ABI does say that the
> -mcmodel=large is strictly only required if the text of a single
> function becomes larger than what the medium model allows.
>
> OTOH, the ABI also doesn't prohibit large sections with -mcmodel=large
> and IMO, the introduction of -mlarge-threshold with -mcmodel=large
> does not create an ABI change.
>
> I think the best way is to first discuss the issue with the x86_64
> psABI group, to clarify how -mlarge-threshold and large data is
> handled under a large code model.
>
> Uros.
Thank you for the suggestion. I started
https://groups.google.com/g/x86-64-abi/c/jnQdJeabxiU ("Large data
sections for the large code model")
and created https://gitlab.com/x86-psABIs/x86-64-ABI/-/merge_requests/42/
to clarify large data sections usage.
In the psABI, "Table 4.4: Additional Special Sections for the Large
Code Model" lists the large data sections.
Perhaps it should be "Table 4.4: Additional Special Sections for the
Medium and Large Code Models".
> >
> > Signed-off-by: Fangrui Song
> > ---
> > gcc/config/i386/i386.cc| 15 +--
> > gcc/config/i386/i386.opt | 2 +-
> > gcc/doc/invoke.texi| 7 ---
> > gcc/testsuite/gcc.target/i386/large-data.c | 13 +
> > 4 files changed, 27 insertions(+), 10 deletions(-)
> > create mode 100644 gcc/testsuite/gcc.target/i386/large-data.c
> >
> > diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> > index a3db55642e3..c68c66a5567 100644
> > --- a/gcc/config/i386/i386.cc
> > +++ b/gcc/config/i386/i386.cc
> > @@ -637,7 +637,8 @@ ix86_can_inline_p (tree caller, tree callee)
> > static bool
> > ix86_in_large_data_p (tree exp)
> > {
> > - if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC)
> > + if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC &&
> > + ix86_cmodel != CM_LARGE && ix86_cmodel != CM_LARGE_PIC)
> > return false;
> >
> >if (exp == NULL_TREE)
> > @@ -848,8 +849,9 @@ x86_elf_aligned_decl_common (FILE *file, tree decl,
> > const char *name, unsigned HOST_WIDE_INT size,
> > unsigned align)
> > {
> > - if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
> > - && size > (unsigned int)ix86_section_threshold)
> > + if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
> > + ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
> > + size > (unsigned int)ix86_section_threshold)
> > {
> >switch_to_section (get_named_section (decl, ".lbss", 0));
> >fputs (LARGECOMM_SECTION_ASM_OP, file);
> > @@ -869,9 +871,10 @@ void
> > x86_output_aligned_bss (FILE *file, tree decl, const char *name,
> > unsigned HOST_WIDE_INT size, unsigned align)
> > {
> > - if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
> > - && size > (unsigned int)ix86_section_threshold)
> > -switch_to_section (get_named_section (decl, ".lbss", 0));
> > + if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
> > + ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
> > + size > (unsigned int)ix86_section_threshold)
> > +switch_to_section(get_named_section(decl, ".lbss", 0));
> >else
> > switch_to_section (bss_section);
> >ASM_OUTPUT_ALIGN (file, floor_log2 (align / BITS_PER_UNIT));
> > diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> > index d74f6b1f8fc..de8e722cd62 100644
> > --- a/gcc/config/i386/i386.opt
> > +++ b/gcc/config/i386/i386.opt
> > @@ -282,7 +282,7 @@ Branches are this expensive (arbitrary units).
> >
> > mlarge-data-threshold=
> > Target RejectNegative Joined UInteger Var(ix86_section_threshold)
> > Init(DEFAULT_LARGE_SECTION_THRESHOLD)
> > --mlarge-data-threshold=Data greater than given threshold
> > will go into .ldata section in x86-64 medium model.
> > +-mlarge-data-threshold=Data greater than given threshold
> > will go into a large data section in x86-64 medium and large code models.
> >
> > mcmodel=
> > Target
Re: [PATCH] i386: Allow -mlarge-data-threshold with -mcmodel=large
On Fri, Apr 28, 2023 at 2:47 AM Fangrui Song wrote:
>
> When using -mcmodel=medium, large data is placed into .l* sections. GNU ld
> places .l* sections into separate output sections. If small and medium
> code model object files are mixed, the .l* sections won't cause
> relocation overflow pressure on sections in -mcmodel=small object files.
>
> However, when using -mcmodel=large, -mlarge-data-threshold doesn't apply.
> This
> means that the .rodata/.data/.bss sections may cause relocation overflow
> pressure on sections in -mcmodel=small object files.
>
> This patch allows -mcmodel=large to generate .l* sections.
The x86_64 psABI does not specify how -mlarge-threshold is handled
with -mcmodel=large and it also doesn't mention that -mcmodel=large
inherits handling from -mcmodel=medium. The ABI does say that the
-mcmodel=large is strictly only required if the text of a single
function becomes larger than what the medium model allows.
OTOH, the ABI also doesn't prohibit large sections with -mcmodel=large
and IMO, the introduction of -mlarge-threshold with -mcmodel=large
does not create an ABI change.
I think the best way is to first discuss the issue with the x86_64
psABI group, to clarify how -mlarge-threshold and large data is
handled under a large code model.
Uros.
>
> Signed-off-by: Fangrui Song
> ---
> gcc/config/i386/i386.cc| 15 +--
> gcc/config/i386/i386.opt | 2 +-
> gcc/doc/invoke.texi| 7 ---
> gcc/testsuite/gcc.target/i386/large-data.c | 13 +
> 4 files changed, 27 insertions(+), 10 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/i386/large-data.c
>
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index a3db55642e3..c68c66a5567 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -637,7 +637,8 @@ ix86_can_inline_p (tree caller, tree callee)
> static bool
> ix86_in_large_data_p (tree exp)
> {
> - if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC)
> + if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC &&
> + ix86_cmodel != CM_LARGE && ix86_cmodel != CM_LARGE_PIC)
> return false;
>
>if (exp == NULL_TREE)
> @@ -848,8 +849,9 @@ x86_elf_aligned_decl_common (FILE *file, tree decl,
> const char *name, unsigned HOST_WIDE_INT size,
> unsigned align)
> {
> - if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
> - && size > (unsigned int)ix86_section_threshold)
> + if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
> + ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
> + size > (unsigned int)ix86_section_threshold)
> {
>switch_to_section (get_named_section (decl, ".lbss", 0));
>fputs (LARGECOMM_SECTION_ASM_OP, file);
> @@ -869,9 +871,10 @@ void
> x86_output_aligned_bss (FILE *file, tree decl, const char *name,
> unsigned HOST_WIDE_INT size, unsigned align)
> {
> - if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
> - && size > (unsigned int)ix86_section_threshold)
> -switch_to_section (get_named_section (decl, ".lbss", 0));
> + if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
> + ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
> + size > (unsigned int)ix86_section_threshold)
> +switch_to_section(get_named_section(decl, ".lbss", 0));
>else
> switch_to_section (bss_section);
>ASM_OUTPUT_ALIGN (file, floor_log2 (align / BITS_PER_UNIT));
> diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> index d74f6b1f8fc..de8e722cd62 100644
> --- a/gcc/config/i386/i386.opt
> +++ b/gcc/config/i386/i386.opt
> @@ -282,7 +282,7 @@ Branches are this expensive (arbitrary units).
>
> mlarge-data-threshold=
> Target RejectNegative Joined UInteger Var(ix86_section_threshold)
> Init(DEFAULT_LARGE_SECTION_THRESHOLD)
> --mlarge-data-threshold=Data greater than given threshold
> will go into .ldata section in x86-64 medium model.
> +-mlarge-data-threshold=Data greater than given threshold
> will go into a large data section in x86-64 medium and large code models.
>
> mcmodel=
> Target RejectNegative Joined Enum(cmodel) Var(ix86_cmodel) Init(CM_32)
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index e5ee2d536fc..4a20eef92e5 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -32927,9 +32927,10 @@ the cache line size. @samp{compat} is the default.
>
> @opindex mlarge-data-threshold
> @item -mlarge-data-threshold=@var{threshold}
> -When @option{-mcmodel=medium} is specified, data objects larger than
> -@var{threshold} are placed in the large data section. This value must be the
> -same across all objects linked into the binary, and defaults to 65535.
> +When @option{-mcmodel=medium} or @option{-mcmodel=large} is specified, data
> +objects larger than
Re: [PATCH] i386: Allow -mlarge-data-threshold with -mcmodel=large
On Thu, Apr 27, 2023 at 5:47 PM Fangrui Song wrote: > > When using -mcmodel=medium, large data is placed into .l* sections. GNU ld > places .l* sections into separate output sections. If small and medium > code model object files are mixed, the .l* sections won't cause > relocation overflow pressure on sections in -mcmodel=small object files. > > However, when using -mcmodel=large, -mlarge-data-threshold doesn't apply. > This > means that the .rodata/.data/.bss sections may cause relocation overflow > pressure on sections in -mcmodel=small object files. > > This patch allows -mcmodel=large to generate .l* sections. > > Signed-off-by: Fangrui Song > --- > [...] Ping https://gcc.gnu.org/pipermail/gcc-patches/2023-April/616947.html :)
[PATCH] i386: Allow -mlarge-data-threshold with -mcmodel=large
When using -mcmodel=medium, large data is placed into .l* sections. GNU ld
places .l* sections into separate output sections. If small and medium
code model object files are mixed, the .l* sections won't cause
relocation overflow pressure on sections in -mcmodel=small object files.
However, when using -mcmodel=large, -mlarge-data-threshold doesn't apply. This
means that the .rodata/.data/.bss sections may cause relocation overflow
pressure on sections in -mcmodel=small object files.
This patch allows -mcmodel=large to generate .l* sections.
Signed-off-by: Fangrui Song
---
gcc/config/i386/i386.cc| 15 +--
gcc/config/i386/i386.opt | 2 +-
gcc/doc/invoke.texi| 7 ---
gcc/testsuite/gcc.target/i386/large-data.c | 13 +
4 files changed, 27 insertions(+), 10 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/large-data.c
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index a3db55642e3..c68c66a5567 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -637,7 +637,8 @@ ix86_can_inline_p (tree caller, tree callee)
static bool
ix86_in_large_data_p (tree exp)
{
- if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC)
+ if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC &&
+ ix86_cmodel != CM_LARGE && ix86_cmodel != CM_LARGE_PIC)
return false;
if (exp == NULL_TREE)
@@ -848,8 +849,9 @@ x86_elf_aligned_decl_common (FILE *file, tree decl,
const char *name, unsigned HOST_WIDE_INT size,
unsigned align)
{
- if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
- && size > (unsigned int)ix86_section_threshold)
+ if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
+ ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
+ size > (unsigned int)ix86_section_threshold)
{
switch_to_section (get_named_section (decl, ".lbss", 0));
fputs (LARGECOMM_SECTION_ASM_OP, file);
@@ -869,9 +871,10 @@ void
x86_output_aligned_bss (FILE *file, tree decl, const char *name,
unsigned HOST_WIDE_INT size, unsigned align)
{
- if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
- && size > (unsigned int)ix86_section_threshold)
-switch_to_section (get_named_section (decl, ".lbss", 0));
+ if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
+ ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
+ size > (unsigned int)ix86_section_threshold)
+switch_to_section(get_named_section(decl, ".lbss", 0));
else
switch_to_section (bss_section);
ASM_OUTPUT_ALIGN (file, floor_log2 (align / BITS_PER_UNIT));
diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
index d74f6b1f8fc..de8e722cd62 100644
--- a/gcc/config/i386/i386.opt
+++ b/gcc/config/i386/i386.opt
@@ -282,7 +282,7 @@ Branches are this expensive (arbitrary units).
mlarge-data-threshold=
Target RejectNegative Joined UInteger Var(ix86_section_threshold)
Init(DEFAULT_LARGE_SECTION_THRESHOLD)
--mlarge-data-threshold=Data greater than given threshold will
go into .ldata section in x86-64 medium model.
+-mlarge-data-threshold=Data greater than given threshold will
go into a large data section in x86-64 medium and large code models.
mcmodel=
Target RejectNegative Joined Enum(cmodel) Var(ix86_cmodel) Init(CM_32)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index e5ee2d536fc..4a20eef92e5 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -32927,9 +32927,10 @@ the cache line size. @samp{compat} is the default.
@opindex mlarge-data-threshold
@item -mlarge-data-threshold=@var{threshold}
-When @option{-mcmodel=medium} is specified, data objects larger than
-@var{threshold} are placed in the large data section. This value must be the
-same across all objects linked into the binary, and defaults to 65535.
+When @option{-mcmodel=medium} or @option{-mcmodel=large} is specified, data
+objects larger than @var{threshold} are placed in large data sections. This
+value must be the same across all objects linked into the binary, and defaults
+to 65535.
@opindex mrtd
@item -mrtd
diff --git a/gcc/testsuite/gcc.target/i386/large-data.c
b/gcc/testsuite/gcc.target/i386/large-data.c
new file mode 100644
index 000..09a917431d4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/large-data.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target lp64 } */
+/* { dg-options "-O2 -mcmodel=large -mlarge-data-threshold=4" } */
+/* { dg-final { scan-assembler ".lbss" } } */
+/* { dg-final { scan-assembler ".bss" } } */
+/* { dg-final { scan-assembler ".ldata" } } */
+/* { dg-final { scan-assembler ".data" } } */
+/* { dg-final { scan-assembler ".lrodata" } } */
+/* { dg-final { scan-assembler ".rodata" } } */
+
+const char rodata_a[] = "abc", rodata_b[] = "abcd";
+char
