Re: AArch64 calling convention in assembly code
"Richard Earnshaw (lists)" <[email protected]>
| Newsgroups | gmane.comp.lib.newlib,gmane.comp.gdb.devel |
|---|---|
| Message-ID | <[email protected]> |
On 01/08/18 14:28, Alexander Fedotov wrote: >>> Pushing LR on the stack resolves a problem > FP of course, not LR. > So the correct code must be like this: > > _cpu_init_hook: > stp x29, x30, [sp, #-16]! > mov x29, sp > bl _init_vectors > bl _flat_map > ldp x29, x30, [sp], #16 > ret > > But still my point is that GDB should catch such an error and do not hang. > > Alex > > On Tue, Jul 31, 2018 at 9:34 PM, Alexander Fedotov <[email protected]> wrote: >> 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. X30 is LR. All we really need is a CFI unwind record that GDB can understand. R. >> >> So my message is that: >> 1. Current code in _cpu_init_hook is incorrect >> 2. GDB should handle this and do not hang >> >> Alex > > >