* [PATCH] Fix CFI interpretation for locations on DW_CFA_*_loc boundaries
@ 2018-11-01 8:49 Milian Wolff
2018-11-01 9:12 ` Milian Wolff
0 siblings, 1 reply; 3+ messages in thread
From: Milian Wolff @ 2018-11-01 8:49 UTC (permalink / raw)
To: elfutils-devel; +Cc: mark, Milian Wolff
According to the DWARF v3 standard §6.4.3 3., all call frame
instructions up to L1 <= L2 should be interpreted for an FDE.
Elfutils currently only interprets L1 < L2, potentially missing
some instructions when L1 directly points at a DW_CFA_*_loc boundary.
This patch changes the behavior and makes elfutils behave like
libunwind in that regard.
---
libdw/cfi.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libdw/cfi.c b/libdw/cfi.c
index 341e055b..332c6b8b 100644
--- a/libdw/cfi.c
+++ b/libdw/cfi.c
@@ -125,7 +125,7 @@ execute_cfi (Dwarf_CFI *cache,
fs->regs[regno].value = (r_value); \
} while (0)
- while (program < end)
+ while (program <= end)
{
uint8_t opcode = *program++;
Dwarf_Word regno;
--
2.19.1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Fix CFI interpretation for locations on DW_CFA_*_loc boundaries
2018-11-01 8:49 [PATCH] Fix CFI interpretation for locations on DW_CFA_*_loc boundaries Milian Wolff
@ 2018-11-01 9:12 ` Milian Wolff
2018-11-01 12:32 ` Milian Wolff
0 siblings, 1 reply; 3+ messages in thread
From: Milian Wolff @ 2018-11-01 9:12 UTC (permalink / raw)
To: elfutils-devel; +Cc: mark
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Please ignore this patch for now - I only looked at one specific case where
this changed the behavior to be in line with libunwind. Sadly, it breaks other
previously working situations. I need to look at this in more detail.
Cheers
On Donnerstag, 1. November 2018 09:48:18 CET Milian Wolff wrote:
> According to the DWARF v3 standard §6.4.3 3., all call frame
> instructions up to L1 <= L2 should be interpreted for an FDE.
> Elfutils currently only interprets L1 < L2, potentially missing
> some instructions when L1 directly points at a DW_CFA_*_loc boundary.
>
> This patch changes the behavior and makes elfutils behave like
> libunwind in that regard.
> ---
> libdw/cfi.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libdw/cfi.c b/libdw/cfi.c
> index 341e055b..332c6b8b 100644
> --- a/libdw/cfi.c
> +++ b/libdw/cfi.c
> @@ -125,7 +125,7 @@ execute_cfi (Dwarf_CFI *cache,
> fs->regs[regno].value = (r_value); \
> } while (0)
>
> - while (program < end)
> + while (program <= end)
> {
> uint8_t opcode = *program++;
> Dwarf_Word regno;
--
Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt, C++ and OpenGL Experts
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Fix CFI interpretation for locations on DW_CFA_*_loc boundaries
2018-11-01 9:12 ` Milian Wolff
@ 2018-11-01 12:32 ` Milian Wolff
0 siblings, 0 replies; 3+ messages in thread
From: Milian Wolff @ 2018-11-01 12:32 UTC (permalink / raw)
To: elfutils-devel; +Cc: mark
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On Donnerstag, 1. November 2018 10:12:41 CET Milian Wolff wrote:
> Please ignore this patch for now - I only looked at one specific case where
> this changed the behavior to be in line with libunwind. Sadly, it breaks
> other previously working situations. I need to look at this in more detail.
Yep, that patch is indeed utterly broken - please ignore it and excuse the
noise.
I was apparently very confused by the different access patterns in libunwind
vs. elfutils. Elfutils is validating every location referenced in the FDE (cf.
frame_unwind.c:501). Libunwind on the other hand doesn't do this - it only
accesses the memory to read the location referenced by the return address
register.
Cheers
> On Donnerstag, 1. November 2018 09:48:18 CET Milian Wolff wrote:
> > According to the DWARF v3 standard §6.4.3 3., all call frame
> > instructions up to L1 <= L2 should be interpreted for an FDE.
> > Elfutils currently only interprets L1 < L2, potentially missing
> > some instructions when L1 directly points at a DW_CFA_*_loc boundary.
> >
> > This patch changes the behavior and makes elfutils behave like
> > libunwind in that regard.
> > ---
> >
> > libdw/cfi.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libdw/cfi.c b/libdw/cfi.c
> > index 341e055b..332c6b8b 100644
> > --- a/libdw/cfi.c
> > +++ b/libdw/cfi.c
> > @@ -125,7 +125,7 @@ execute_cfi (Dwarf_CFI *cache,
> >
> > fs->regs[regno].value = (r_value); \
> >
> > } while (0)
> >
> > - while (program < end)
> > + while (program <= end)
> >
> > {
> >
> > uint8_t opcode = *program++;
> > Dwarf_Word regno;
--
Milian Wolff
mail@milianw.de
http://milianw.de
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