Re: [PATCH 2/3] Unwind support for ARM EABI

[Timo Teras <timo.teras@iki.fi>]

On Wed, 10 Jul 2013 16:39:00 +0300
Timo Teräs <timo.teras@iki.fi> wrote:

> ARM EABI does not use the .eh_frame and .eh_frame_hdr for unwinding.
> Instead the ABI specifies it's own way to unwind using .ARM.exidx and
> .ARM.extab.
> 
> libgcc uses __gnu_Unwind_Find_exidx (libc must implement this) when
> unwinding using exidx. This function is implemented here.
> ---
>  arch/arm/src/find_exidx.c | 44
> ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44
> insertions(+) create mode 100644 arch/arm/src/find_exidx.c
> 
> diff --git a/arch/arm/src/find_exidx.c b/arch/arm/src/find_exidx.c
> new file mode 100644
> index 0000000..ffbea1f
> --- /dev/null
> +++ b/arch/arm/src/find_exidx.c
> @@ -0,0 +1,44 @@
> +#define _GNU_SOURCE
> +#include <link.h>
> +
> +typedef unsigned _Unwind_Ptr;

As noted on #musl, this has  __attribute__((pointer)) in the original
definition. But trying to avoid the #include <unwind.h> on GCC's
headers, and the GCCisms. 

Would uintptr_t be more suitable here then?

> +struct find_exidx_data {
> +	_Unwind_Ptr pc, exidx_start;
> +	int exidx_len;
> +};
> +
> +static int find_exidx(struct dl_phdr_info *info, size_t size, void
> *ptr) +{
> +	struct find_exidx_data *data = ptr;
> +	const ElfW(Phdr) *phdr = info->dlpi_phdr;
> +	_Unwind_Ptr addr;
> +	int match = 0, i;
> +
> +	for (i = info->dlpi_phnum; i > 0; i--, phdr++) {
> +		addr = info->dlpi_addr + phdr->p_vaddr;
> +		switch (phdr->p_type) {
> +		case PT_LOAD:
> +			match |= data->pc >= addr && data->pc < addr
> + phdr->p_memsz;
> +			break;
> +		case PT_ARM_EXIDX:
> +			data->exidx_start = addr;
> +			data->exidx_len = phdr->p_memsz;
> +			break;
> +		}
> +	}
> +	return match;
> +}

The above function has a slight bug in it, so I'll fix that for next
send. Basically it can return other dso's exidx data if the matching
dso did not have PT_ARM_EXIDX at all.

- Timo