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Re: [PATCH][V2] Change calling convention of dwarf_getmacros to allow opcode 0xff
- From: Petr Machata <pmachata at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Wed, 10 Dec 2014 01:45:03 +0100
- Subject: Re: [PATCH][V2] Change calling convention of dwarf_getmacros to allow opcode 0xff
Mark Wielaard <email@example.com> writes:
> On Mon, 2014-12-08 at 14:23 +0100, Petr Machata wrote:
>> + /* Make sure the offset didn't overflow into the flag bit. */
>> + assert ((offset & DWARF_GETMACROS_START) == 0);
> Very unlikely, but theoretically a valid thing that might happen I
> assume. I am not a fan of asserts in library code in this case. Could we
> signal an DWARF_E_INVALID_OFFSET error and return -1 instead? If this
> could theoretically happen could you change the code to signal an error
> and return -1 before committing. Otherwise just say it won't happen and
> commit as is.
It might happen for macro sections that are larger than half of host
address space (e.g. 2G for 32-bit libdw). The offset would then be
negative, but adding it to the data start would wrap around and do the
right thing, I think. So it's the fact that we need that one bit for
something else that's limiting us here.
How about this?
diff --git a/libdw/dwarf_getmacros.c b/libdw/dwarf_getmacros.c
index 0ba3854..bd64d60 100644
@@ -407,7 +407,11 @@ token_from_offset (ptrdiff_t offset, bool accept_0xff)
/* Make sure the offset didn't overflow into the flag bit. */
- assert ((offset & DWARF_GETMACROS_START) == 0);
+ if ((offset & DWARF_GETMACROS_START) != 0)
+ __libdw_seterrno (DWARF_E_TOO_BIG);
+ return -1;
offset |= DWARF_GETMACROS_START;