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POdladdr doesnt return the function name
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  1. POdladdr doesnt return the function name
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    copied!<p>I'm trying to use dladdr. It correctly locates the library, but it does not find the function name. I can call objdump, do a little math, and get the address of the function that I pass dladdr. If objdump can see it, why can't dladdr?</p> <p>Here is my function:</p> <pre><code>const char *FuncName(const void *pFunc) { Dl_info DlInfo; int nRet; // Lookup the name of the function given the function pointer if ((nRet = dladdr(pFunc, &amp;DlInfo)) != 0) return DlInfo.dli_sname; return NULL; } </code></pre> <p>Here is a gdb transcript showing what I get.</p> <pre><code>Program received signal SIGINT, Interrupt. [Switching to Thread 0xf7f4c6c0 (LWP 28365)] 0xffffe410 in __kernel_vsyscall () (gdb) p MatchRec8Cmp $2 = {void (TCmp *, TWork *, TThread *)} 0xf1b62e73 &lt;MatchRec8Cmp&gt; (gdb) call FuncName(MatchRec8Cmp) $3 = 0x0 (gdb) call FuncName(0xf1b62e73) $4 = 0x0 (gdb) b FuncName Breakpoint 1 at 0xf44bdddb: file threads.c, line 3420. (gdb) call FuncName(MatchRec8Cmp) Breakpoint 1, FuncName (pFunc=0xf1b62e73) at threads.c:3420 3420 { The program being debugged stopped while in a function called from GDB. When the function (FuncName) is done executing, GDB will silently stop (instead of continuing to evaluate the expression containing the function call). (gdb) s 3426 if ((nRet = dladdr(pFunc, &amp;DlInfo)) != 0) (gdb) 3427 return DlInfo.dli_sname; (gdb) p DlInfo $5 = {dli_fname = 0x8302e08 "/xxx/libdata.so", dli_fbase = 0xf1a43000, dli_sname = 0x0, dli_saddr = 0x0} (gdb) p nRet $6 = 1 (gdb) p MatchRec8Cmp - 0xf1a43000 $7 = (void (*)(TCmp *, TWork *, TThread *)) 0x11fe73 (gdb) q The program is running. Exit anyway? (y or n) y </code></pre> <p>Here is what I get from objdmp</p> <pre><code>$ objdump --syms /xxx/libdata.so | grep MatchRec8Cmp 0011fe73 l F .text 00000a98 MatchRec8Cmp </code></pre> <p>Sure enough, 0011fe73 = MatchRec8Cmp - 0xf1a43000. Anyone know why dladdr can't return dli_sname = "MatchRec8Cmp" ???</p> <p>I'm running Red Hat Enterprise Linux Server release 5.4 (Tikanga). I have seen this work before. Maybe it's my compile switches:</p> <pre><code>CFLAGS = -m32 -march=i686 -msse3 -ggdb3 -pipe -fno-common -fomit-frame-pointer \ -Ispio -fms-extensions -Wmissing-declarations -Wstrict-prototypes -Wunused -Wall \ -Wno-multichar -Wdisabled-optimization -Wmissing-prototypes -Wnested-externs \ -Wpointer-arith -Wextra -Wno-sign-compare -Wno-sequence-point \ -I../../../include -I/usr/local/include -fPIC \ -D$(Uname) -D_REENTRANT -D_GNU_SOURCE </code></pre> <p>I have tried it with -g instead of -ggdb3 although I don't think debugging symbols have anything to do with elf.</p> <p>Thanks!</p>
 

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