Hello, Recently I'm getting lot's of "invalid read/invalid write" valgrind errors which point out at memory allocated for the stack. However the code doesn't crush and finish running successfully. I'm trying to understand where the error comes from - and will be grateful fo any help wih this issue. Here's what I can see using vgdb:
(gdb) monitor v.info last_error ==10259== Invalid write of size 4 ==10259== at 0x28686C: vsnprintf (in /lib/libc-2.12.so) ==10259== Address 0x4b43040 is 45,120 bytes inside a block of size 65,536 alloc'd ==10259== at 0x4005DB9: memalign (vg_replace_malloc.c:727) ==10259== by 0x4005E68: posix_memalign (vg_replace_malloc.c:876) -The memory for the stack is allocated using memalign and then the upper and lower parts of it are protected using mprotect, so the stack looks like this: 16k protected with mprotect, 32K valid for usage, another 16K protected. The problem happens only in the valid area. -The problem always seems to happen in the end of the first page of the valid memory. For example, the stack above starts with the address 0x4b44000 and goes down, the first inaccessible address is 0x4b4304b. -The address pointed out as inaccessible is above the stack pointer: (gdb) info registers eax 0x100 256 ecx 0x0 0 edx 0x0 0 ebx 0x3acff4 3854324 esp 0x4b42f44 0x4b42f44 ebp 0x4b4304c 0x4b4304c esi 0x4b43b70 78920560 edi 0x4b431d4 78918100 eip 0x28686c 0x28686c <vsnprintf+12> -Even though addressibility is not supposed to be affected by mprotect, when I comment out the calls to mprotect the poblem doen't happen any more. -There's no specific line in the code that is causing the problem. It seems that he problem always happens in the end of the first page of the stack. I tried checkig the memory at the point of allocation - and the pointed out address is valid. It also seems valid when the thread starts running and becoms invalid only when the stack reaches near 4K. Considering the fact there's no crash in the program and it runs normally and correctly in spite of those errors, I don't understand what is the reason of valgrind componains. Any help with the cause of the problem or with further evaluation will be highly appreciated, as after spending a few days on this I'm run out of ideas. Thank you, Masha. -- View this message in context: http://valgrind.10908.n7.nabble.com/Valgrind-shows-Invalid-write-os-size-4-for-memory-allocated-for-the-stack-tp45597.html Sent from the Valgrind - Users mailing list archive at Nabble.com. ------------------------------------------------------------------------------ How ServiceNow helps IT people transform IT departments: 1. A cloud service to automate IT design, transition and operations 2. Dashboards that offer high-level views of enterprise services 3. A single system of record for all IT processes http://p.sf.net/sfu/servicenow-d2d-j _______________________________________________ Valgrind-users mailing list Valgrind-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/valgrind-users
