When I build Python 3.12.4 with --enable-shared option:
Enable building a shared Python library: libpython (default is no).
the only output I get from ltrace is:
Py_BytesMain(2, 0x7ffd1e465518, 0x7ffd1e465530, 0x649272aa9da0) = 0
+++ exited (status 0) +++
If the option is not used, ltrace works as expected.
Why is it happening? How can I troubleshoot it?
My config:
From man ltrace:
-e filter
A qualifying expression which modifies which library calls to trace.
...
If no -e is given, @MAIN is assumed as a default.
That is: if you don't pass -e, then only calls from the main binary are traced.
When you build Python with --enable-shared, the (tiny) python binary only calls the Py_BytesMain (which is in libpython.so), and the rest of the execution continues in that shared library, which is filtered out due to the assumed default filter.
To fix this, use -e '@*'.
Here is a simple example demonstrating the problem:
// foo.c
#include <stdio.h>
int foo()
{
puts("Hello");
return 42;
}
// main.c
extern int foo();
int main() { return foo(); }
gcc -fPIC -shared -o foo.so foo.c && gcc main.c ./foo.so
ltrace ./a.out
foo(1, 0x7ffef092d2f8, 0x7ffef092d308, 0x559054ea9dc8Hello
) = 42
+++ exited (status 42) +++
ltrace -e '@*' ./a.out
libc.so.6->(0x7f730193b2c0, 0, 0x7ffd369fa3b8, 0x5625cd742dc8) = 0
a.out->foo(1, 0x7ffd369fa3a8, 0x7ffd369fa3b8, 0x5625cd742dc8 <unfinished ...>
foo.so->puts("Hello" <unfinished ...>
libc.so.6->(0x7f7301903000, 0x7ffd369fa3a8, 0x7ffd369fa3b8, 0x5625cd742dc8) = 5
libc.so.6->(31, 0x7ffd369fa090, 0x7f7301799930, 0x7f73018dab20) = 465
libc.so.6->(24, 0x7ffd369fa090, 0x7f7301799950, 0x7f73019387e0) = 360
libc.so.6->(1, 0x7ffd369fa090, 0x7f73017998f0, 0x7f73019387e0) = 15
libc.so.6->(14, 0x7ffd369fa090, 0x7f7301799960, 0x7f73019387e0) = 210
libc.so.6->(12, 0x7ffd369fa090, 0x7f7301799910, 0x7f73019387e0) = 180
libc.so.6->(36, 0x7ffd369fa090, 0x7f7301799980, 0x7f73019387e0) = 540
libc.so.6->(21, 0x7ffd369fa090, 0x7f7301799990, 0x7f73019387e0) = 315
libc.so.6->(2, 0x7ffd369fa090, 0x7f73017999a0, 0x7f73019387e0) = 30
libc.so.6->(25, 0x7ffd369fa090, 0x7f73017999e0, 0x7f73019387e0) = 375
libc.so.6->(5, 0x7ffd369fa090, 0x7f7301799a00, 0x7f73019387e0) = 75
libc.so.6->(0, 0x7ffd369fa090, 0x7f7301799a10, 0x7f73019387e0) = 0
libc.so.6->(22, 0x7ffd369fa090, 0x7f7301799c40, 0x7f73019387e0) = 330
Hello
<... puts resumed> ) = 6
<... foo resumed> ) = 42
+++ exited (status 42) +++