https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101383
Bug ID: 101383
Summary: GCC 11 Reproducibility Issue
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
Assignee: unassigned at gcc dot gnu.org
Reporter: toolybird at tuta dot io
Target Milestone: ---
Performing 2 consecutive runs of a normal 3-stage bootstrap results in
differing cc1 and cc1plus binaries.
This appears to be a regression since GCC 10 does not exhibit the problem.
The issue can be pinpointed to cc1-checksum.c and cc1plus-checksum.c
I know very little about this stuff but I suspect the root cause is due to the
move to DWARF 5
Please note: This is a standard `make' which means default BOOT_CFLAGS of "-g
-O2".
Comparing the saved object files between runs with `readelf -w' reveals
differences with GCC 11 whereas with GCC 10 they are identical. For example
with GCC 11:
$ cmp -lb gcc-build.1st/prev-gcc/c/c-lang.o gcc-build.2nd/prev-gcc/c/c-lang.o
1932 130 X 114 L
1933 62 2 60 0
1934 171 y 142 b
1935 127 W 71 9
1936 150 h 153 k
1937 121 Q 126 V
1943 130 X 114 L
1944 62 2 60 0
1945 171 y 142 b
1946 127 W 71 9
1947 150 h 153 k
1948 121 Q 126 V
2066 130 X 114 L
2067 62 2 60 0
2068 171 y 142 b
2069 127 W 71 9
2070 150 h 153 k
2071 121 Q 126 V
$ readelf -w gcc-build.1st/prev-gcc/c/c-lang.o > 1.txt
$ readelf -w gcc-build.2nd/prev-gcc/c/c-lang.o > 2.txt
$ diff -u 1.txt 2.txt
--- 1.txt 2021-07-09 17:20:09.504532430 +1000
+++ 2.txt 2021-07-09 17:20:26.174675615 +1000
@@ -34,8 +34,8 @@
The File Name Table (offset 0x30, lines 2, columns 2):
Entry Dir Name
- 0 0 (indirect line string, offset: 0xa): ccX2yWhQ.s
- 1 1 (indirect line string, offset: 0x15): ccX2yWhQ.s
+ 0 0 (indirect line string, offset: 0xa): ccL0b9kV.s
+ 1 1 (indirect line string, offset: 0x15): ccL0b9kV.s
Line Number Statements:
[0x0000003a] Extended opcode 2: set Address to 0x0
@@ -55,8 +55,8 @@
Contents of the .debug_line_str section:
- 0x00000000 2f746d70 002f746d 70006363 58327957 /tmp./tmp.ccX2yW
- 0x00000010 68512e73 00636358 32795768 512e7300 hQ.s.ccX2yWhQ.s.
+ 0x00000000 2f746d70 002f746d 70006363 4c306239 /tmp./tmp.ccL0b9
+ 0x00000010 6b562e73 0063634c 3062396b 562e7300 kV.s.ccL0b9kV.s.
<...snip...>
>From looking at the Makefiles, it appears `cc1-checksum.c' is copied from the
previous stage for some reason, which I think might be pertinent. It also seems
like different flags are used between stages 2 and 3:
-DIN_GCC_FRONTEND -g -O2 -fno-checking -gtoggle -DIN_GCC
-DIN_GCC_FRONTEND -g -O2 -fchecking=1 -DIN_GCC
Any comments? Thanks.
