https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98692
Bug ID: 98692
Summary: Unitialized Values reported only with -Os
Product: gcc
Version: 10.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: nick.child at ibm dot com
Target Milestone: ---
Host: powerpcle-*-linux-gnu*
Target: powerpcle-*-linux-gnu*
Build: powerpcle-*-linux-gnu*
Created attachment 49970
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49970&action=edit
Preprocesssed File
Hello all,
This is my first go at something like this so I apologize for any cringes now.
Recently, I implemented memory checks into our CI using valgrind. Everything
works fine on x86 with the same commands but gives issues when running on
POWER. Specifically, only when using the `-Os` size optimizer flag. Things like
`O2` and `O3` don't bring about any errors. While the code runs fine, these
valgrind errors are a bit alarming. I have run into the issue using the
following compiler versions and OS's:
gcc version 9.3.1 20200408 (Red Hat 9.3.1-2)
gcc version 10.2.1 20200723 (Red Hat 10.2.1-1)
gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)
The errors revolve around an conditional jump on unitialized variables. I am
thinking it is a stack allocation issue. I have tried to narrow down my issue
to as simple a program as possible (attached).
I then build using:
$ gcc -Os issue.c -o issue
Compilation works and binary executes normally but valgrind complains with:
$ valgrind ./issue
This could very well be a valgrind mistake, with too many things being
optimized off of the executable for valgrind to accurately keep track of
memory.
Here is the output from valgrind:
==3557285== Using Valgrind-3.16.1 and LibVEX; rerun with -h for copyright info
==3557285== Command: leak
==3557285==
==3557285== Conditional jump or move depends on uninitialised value(s)
==3557285== at 0x416E9B8: __vfprintf_internal (vfprintf-internal.c:1332)
==3557285== by 0x415E33B: printf@@GLIBC_2.17 (printf.c:33)
==3557285== by 0x100005D3: main (in /home/jenkins/testPlace/test2/leak)
==3557285==
==3557285== Use of uninitialised value of size 8
==3557285== at 0x40A14DC: strchrnul (vg_replace_strmem.c:1394)
==3557285== by 0x416E9D3: __find_specmb (printf-parse.h:111)
==3557285== by 0x416E9D3: __vfprintf_internal (vfprintf-internal.c:1365)
==3557285== by 0x415E33B: printf@@GLIBC_2.17 (printf.c:33)
==3557285== by 0x100005D3: main (in /home/jenkins/testPlace/test2/leak)
==3557285==
==3557285== Use of uninitialised value of size 8
==3557285== at 0x40A14F0: strchrnul (vg_replace_strmem.c:1394)
==3557285== by 0x416E9D3: __find_specmb (printf-parse.h:111)
==3557285== by 0x416E9D3: __vfprintf_internal (vfprintf-internal.c:1365)
==3557285== by 0x415E33B: printf@@GLIBC_2.17 (printf.c:33)
==3557285== by 0x100005D3: main (in /home/jenkins/testPlace/test2/leak)
==3557285==
==3557285== Conditional jump or move depends on uninitialised value(s)
==3557285== at 0x418BABC: _IO_file_xsputn@@GLIBC_2.17 (fileops.c:1204)
==3557285== by 0x416EA33: __vfprintf_internal (vfprintf-internal.c:1373)
==3557285== by 0x415E33B: printf@@GLIBC_2.17 (printf.c:33)
==3557285== by 0x100005D3: main (in /home/jenkins/testPlace/test2/leak)
==3557285==
==3557285== Conditional jump or move depends on uninitialised value(s)
==3557285== at 0x418BC94: _IO_new_file_xsputn (fileops.c:1253)
==3557285== by 0x418BC94: _IO_file_xsputn@@GLIBC_2.17 (fileops.c:1197)
==3557285== by 0x416EA33: __vfprintf_internal (vfprintf-internal.c:1373)
==3557285== by 0x415E33B: printf@@GLIBC_2.17 (printf.c:33)
==3557285== by 0x100005D3: main (in /home/jenkins/testPlace/test2/leak)
==3557285==
...
...
...
==3558101==
==3558101== HEAP SUMMARY:
==3558101== in use at exit: 0 bytes in 0 blocks
==3558101== total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==3558101==
==3558101== All heap blocks were freed -- no leaks are possible
==3558101==
==3558101== Use --track-origins=yes to see where uninitialised values come from
==3558101== For lists of detected and suppressed errors, rerun with: -s
==3558101== ERROR SUMMARY: 44 errors from 31 contexts (suppressed: 0 from 0)
