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AArch64 calling convention in assembly code
- From: Alexander Fedotov <alfedotov at gmail dot com>
- To: newlib at sourceware dot org, bug-gdb at gnu dot org
- Date: Tue, 31 Jul 2018 21:34:07 +0300
- Subject: AArch64 calling convention in assembly code
Hello dear AArch64 maintainers
Please look into code snippet below from newlib/libgloss/aarch64/rdimon-aem-el3.
Seems to me this code violates AArch64 calling convention and actually
breaks debugging in GDB. GDB tries to unwind call stack and got
endless reentrancy...
FUNCTION (_cpu_init_hook):
sub sp, sp, #16
str x30, [sp, xzr]
bl _init_vectors
bl _flat_map
ldr x30, [sp, xzr]
add sp, sp, #16
ret
We have couple of calls there (_init_vectors, _flat_map). If you'll
try to step into any subroutine you will found that GDB hangs and
can't step anymore.
Pushing LR on the stack resolves a problem.
So my message is that:
1. Current code in _cpu_init_hook is incorrect
2. GDB should handle this and do not hang
Alex