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Date: Wed, 10 Jul 2013 20:35:18 +0300
From: Timo Teras <timo.teras@....fi>
To: musl@...ts.openwall.com
Subject: Re: [PATCH 2/3] Unwind support for ARM EABI
On Wed, 10 Jul 2013 16:39:00 +0300
Timo Teräs <timo.teras@....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
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