https://bugs.kde.org/show_bug.cgi?id=384930
Bug ID: 384930
Summary: Valgrind fails to compute correctly some code using
the GMP library
Product: valgrind
Version: 3.13.0
Platform: Debian testing
OS: Linux
Status: UNCONFIRMED
Severity: major
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 107934
--> https://bugs.kde.org/attachment.cgi?id=107934&action=edit
bug.c
When I run the simple program obtained from the source file bug.c in
attachment, I obtain different results depending on whether it is run under
valgrind or not.
When it is not run under valgrind, I obtain the expected values (lcm (2^i,
42)), when it is run under valgrind, the values obtained are false for large i.
I suspect that for large value of i, 2^i exceed a threshold in the GMP library
code and that some asm code is used. It may be that the asm code in not
correctly emulate by valgrind.
How to reproduce the code:
GMP version: 6.1.2 (configured and compiled with gmp-mparam.h ->
mpn/x86_64/skylake/gmp-mparam.h)
$ gcc -o bug bug.c -lgmp -lm
$ ./bug > normal
$ valgrind ./bug > valgrind
$ cmp normal valgrind
normal valgrind differ: byte 339003, line 1469
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