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I have a issue with gdb printf in version 9.1

echo -e '#include<stdio.h> \n int main(){ \n printf("Hello"); \n }' > test.c gcc -g test.c -o test echo 'break test.c:4' > test.gdb echo 'run' >> test.gdb echo 'set $aux = (char*)malloc(256)' >> test.gdb echo 'set $e = strcpy($aux, "abc")' >> test.gdb echo 'printf "%s", $aux' >> test.gdb gdb --batch --command=test.gdb test

Output with gdb 9.1:

Breakpoint 1 at 0x1167: file test.c, line 4. Breakpoint 1, main () at test.c:4 4 } �e���

Expected output (same as gdb v8):

Breakpoint 1 at 0x1167: file test.c, line 4. Breakpoint 1, main () at test.c:4 4 } abc

I've checked charset, but it seems ok. Any idea about that?

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This is Bug 25650 - GDB can't 'printf' a convenience variable holding an inferior address, fixed in gdb 9.2.

If you can't upgrade to gdb 9.2 but can recompile your existing distro's gdb 9.1, there is a two-line patch.

On Ubuntu 20.04, which comes with gdb 9.1-0ubuntu1:

  1. run apt build-dep gdb to haul in the packages needed to build gdb from source
  2. run apt install dpkg-dev (to get /usr/bin/dpkg-source)
  3. uncomment the deb-src lines in /etc/apt/sources.list
  4. run apt update
  5. cd to an empty directory and run apt source gdb . Doing this in a fresh new directory will make it easier to clean things up after the compilation.
  6. cd to gdb-9.1 and apply the patch to gdb/printcmd.c
  7. build and install gdb. For example, to put it in /usr/local/bin, the default, you'd run
 mkdir build cd build ../configure make make install
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