ARM EABI / Thumb vs. gdb

[Khem Raj]

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Johannes Stezenbach wrote:
> Hi,
> 
> I've built an ARM EABI toolchain with uClibc compiled as
> Thumb code using buildroot (BR2_TARGET_OPTIMIZATION="-Os -mthumb").
> 
> This works fine except that in gdb (6.8), if you stop your program
> with some threads blocked in syscalls, gdb is unable to display
> a call stack for those threads.
> 
> The reason for this is that gdb's calculation of the stack
> frame size is off because of the "push {r7}" used in the syscall code.
> (INTERNAL_SYSCALL in uClibc/libc/sysdeps/linux/arm/bits/syscalls.h)
> 
> Rather than fixing gdb (specifically thumb_analyze_prologue() in
> arm-tdep.c), I made a local change to avoid changing the stack
> pointer in INTERNAL_SYSCALL, like so:
> 
> -      asm volatile ("push       {r7}\n"                         \
> -                    "\tmov      r7, v3\n"                       \
> -                    "\tswi      0       @ syscall " #name "\n"  \
> -                    "\tpop      {r7}"                           \
> 
> +       __asm__ volatile ("push {r7}\n"                         \
> +                    "\tmov     r7, v3\n"                       \
> +                    "\tpop     {v3}\n"                         \
> +                    "\tswi     0       @ syscall " #name "\n"  \
> +                    "\tmov     r7, v3\n"                               \
> 
> But just before posting here I took a peek into the NPTL
> branch and noticed that there is a better patch which avoids
> the "push {r7}" altogether:

Good you found it. otherwise thats what I would have pointed you to.


> 
> 
> Please consider merging this change into trunk.

uclibc-nptl branch soon collapse into trunk so this changeset will make through.

> 
> 
> Thanks,
> Johannes
> _______________________________________________
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> 

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