Valgrind reports use of uninitialised value for __gmpz_powm_sec on i686 host

[Trevor Spiteri]

Valgrind is reporting the use of uninitialised value(s) in 
__gmpz_powm_sec for i686 host, though I found no similar issue for 
x86_64 host. This issue started in 6.3.0, and was not there for 6.2.1.

Please find the details below.

Best regards,
Trevor Spiteri


GMP version 6.3.0 (unpatched) configured on an x86_64 build system using:

gmp-6.3.0/configure --host i686


Configure prints:

configure: summary of build options:

   Version:           GNU MP 6.3.0
   Host type:         i686-pc-none
   ABI:               32
   Install prefix:    /usr/local
   Compiler:          gcc
   Static libraries:  yes
   Shared libraries:  no


Contents of a.c:

#include <gmp.h>
int main(void)
{
   mpz_t base, exp, mod, ret;
   int error_code;
   mpz_init_set_ui(base, 7);
   mpz_init_set_ui(exp, 4);
   mpz_init_set_ui(mod, 13);
   mpz_init(ret);
   mpz_powm_sec(ret, base, exp, mod);
   if (mpz_cmp_ui(ret, 9))
     error_code = 1;
   else
     error_code = 0;
   mpz_clear(ret);
   mpz_clear(mod);
   mpz_clear(exp);
   mpz_clear(base);
   return error_code;
}


Compiled using:

gcc -m32 a.c -I . -L .libs -lgmp


Executing ./a.out returns no error. But "valgrind ./a.out" reports:

==207620== Memcheck, a memory error detector
==207620== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==207620== Using Valgrind-3.21.0 and LibVEX; rerun with -h for copyright info
==207620== Command: ./a.out
==207620==
==207620== Conditional jump or move depends on uninitialised value(s)
==207620==    at 0x8049489: __gmpz_powm_sec (in /home/trevor/scratch/val_gmp/a.out)
==207620==    by 0x804923D: main (in /home/trevor/scratch/val_gmp/a.out)
==207620==
==207620== Conditional jump or move depends on uninitialised value(s)
==207620==    at 0x8049309: __gmpz_cmp_ui (in /home/trevor/scratch/val_gmp/a.out)
==207620==    by 0x804924E: main (in /home/trevor/scratch/val_gmp/a.out)
==207620==
==207620== Conditional jump or move depends on uninitialised value(s)
==207620==    at 0x8049254: main (in /home/trevor/scratch/val_gmp/a.out)
==207620==
==207620==
==207620== HEAP SUMMARY:
==207620==     in use at exit: 0 bytes in 0 blocks
==207620==   total heap usage: 4 allocs, 4 frees, 16 bytes allocated
==207620==
==207620== All heap blocks were freed -- no leaks are possible
==207620==
==207620== Use --track-origins=yes to see where uninitialised values come from
==207620== For lists of detected and suppressed errors, rerun with: -s
==207620== ERROR SUMMARY: 3 errors from 3 contexts (suppressed: 0 from 0)



Additional information:

Distribution:
Fedora 38

gcc-v:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/13/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,m2,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --enable-libstdcxx-backtrace --with-libstdcxx-zoneinfo=/usr/share/zoneinfo --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl=/builddir/build/BUILD/gcc-13.2.1-20230728/obj-x86_64-redhat-linux/isl-install --enable-offload-targets=nvptx-none --without-cuda-driver --enable-offload-defaulted --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux --with-build-config=bootstrap-lto --enable-link-serialization=1
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.2.1 20230728 (Red Hat 13.2.1-1) (GCC)


uname -a:

Linux hawat 6.4.11-200.fc38.x86_64 #1 SMP PREEMPT_DYNAMIC Wed Aug 16 17:42:12 UTC 2023 x86_64 GNU/Linux


gmp-6.3.0/config.guess:

nehalem-pc-linux-gnu


sh gmp-6.3.0/configfsf.guess:

x86_64-pc-linux-gnu


valgrind --version:

valgrind-3.21.0