https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103768
Bug ID: 103768
Summary: array-bounds warning for `memcpy((void*)0x1234, p,
n)`, where n is greater than 8
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: pmenzel+gcc at molgen dot mpg.de
Target Milestone: ---
In the SeaBIOS list thread *[PATCH] memmap: Fix gcc out-of-bounds warning* [1],
the array out of bounds warning below from at least GCC 11.2.0 is discussed:
```
In file included from src/fw/smm.c:18:
src/fw/smm.c: In function 'smm_save_and_copy':
src/string.h:23:16: warning: '__builtin_memcpy' offset [0, 511] is out of the
bounds [0, 0] [-Warray-bounds]
23 | #define memcpy __builtin_memcpy
src/fw/smm.c:148:5: note: in expansion of macro 'memcpy'
148 | memcpy(&smm->cpu, &initsmm->cpu, sizeof(smm->cpu));
| ^~~~~~
src/fw/smm.c: In function 'smm_relocate_and_restore':
src/string.h:23:16: warning: '__builtin_memcpy' offset [0, 511] is out of the
bounds [0, 0] [-Warray-bounds]
23 | #define memcpy __builtin_memcpy
src/fw/smm.c:171:5: note: in expansion of macro 'memcpy'
171 | memcpy(&initsmm->cpu, &smm->cpu, sizeof(initsmm->cpu));
| ^~~~~~
src/fw/smm.c: In function 'handle_smi':
src/string.h:23:16: warning: '__builtin_memcpy' offset [0, 511] is out of the
bounds [0, 0] [-Warray-bounds]
23 | #define memcpy __builtin_memcpy
src/fw/smm.c:88:13: note: in expansion of macro 'memcpy'
88 | memcpy(&newsmm->backup1, &smm->cpu,
sizeof(newsmm->backup1));
| ^~~~~~
src/string.h:23:16: warning: '__builtin_memcpy' offset [0, 511] is out of the
bounds [0, 0] [-Warray-bounds]
23 | #define memcpy __builtin_memcpy
src/fw/smm.c:89:13: note: in expansion of macro 'memcpy'
89 | memcpy(&newsmm->backup2, &smm->cpu,
sizeof(newsmm->backup2));
| ^~~~~~
```
Kevin writes:
> Yes - I see that as well in smm.c. Alas, I don't have a fix for it.
> It seems to me that gcc is producing bogus warnings here. It looks
> like anything of the form "memcpy((void*)0x1234, p, n)" where n is
> greater than 8 produces this warning. It's a requirement to memcpy to
> a physical memory address. Disabling the warning would require adding
> both "-Wno-array-bounds -Wno-stringop-overflow" to the build.
>
> Maybe someone else has an idea on how to suppress this warning.
The SeaBIOS source code is available in a git repository [2]. `make
olddefconfig && make -j$(nproc)` reproduces the warning.
[1]:
https://mail.coreboot.org/hyperkitty/list/[email protected]/thread/KCV5A4GZQDFNANU7QZYR4Y6ZNFGMEJQN/
[2]:
https://review.coreboot.org/plugins/gitiles/seabios/+/refs/tags/rel-1.15.0/src/fw/smm.c#148
