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I am wondering how do I print out data through advanced indexing in GDB? For example, say I want to print out the value at 8(%ebp) to get the first parameter passed into a function. How would I do that? The following command does not seem to work:

p (int)8 ($esp)

I always get this segmentation fault error:

Program received signal SIGSEGV, Segmentation fault. 0x00000008 in ?? () The program being debugged was signaled while in a function called from GDB. GDB remains in the frame where the signal was received. To change this behavior use "set unwindonsignal on". Evaluation of the expression containing the function (at 0x0x8) will be abandoned. When the function is done executing, GDB will silently stop.

Adam Lee
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    You need to turn the assembler syntax into a gdb expression. Also, you need to examine memory. Something like `x $esp+8`. Add format specifiers as appropriate. – Jester Nov 28 '20 at 12:20
  • Related: [How to print memory referenced by a complex addressing mode, using GDB?](https://stackoverflow.com/q/52998800) – Peter Cordes Dec 22 '22 at 07:41

1 Answers1

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I think 8($esp) tries to call 8 as a function, with %esp as the arg. (But absolute address 8 is not in a valid executable page). Remember that GDB uses GDB's C-like syntax, not AT&T assembly addressing-mode syntax.

Register + offset is hardly "advanced indexing", but regardless, it's easy enough to translate to a GDB expression:

x  $esp + 8

The x command examines memory at that address. Use help x to see options for formatting and how many elements to display. p would print the address, unless you cast it to a pointer and dereference it like p *(int*)(8 + $esp)

Peter Cordes
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