Sorry about the delayed review. I seem to have missed this earlier. On Tue, Mar 25, 2014 at 12:21 PM, Eric Botcazou <ebotca...@adacore.com> wrote: > Hi, > > because of popular demand we switched the Ada compiler to ZCX, i.e. table- > driven EH scheme, on ARM/Linux, only to discover that GCC doesn't generate > correct EH tables, which means that the Ada compiler cannot catch exceptions.
> > See also the earlier message posted by Tristan: > http://gcc.gnu.org/ml/gcc/2013-12/msg00157.html > > The problem is the discrepancy between the declared encoding and the actual > encoding of the TType. The latter is specified by the EABI: symbols must be > relocated with an R_ARM_TARGET2 relocation, as visible in the assembly: > > .LLSDACSE0: > .byte 0x1 @ Action record table > .byte 0 > .align 2 > .word _ZTIi(TARGET2) > > R_ARM_TARGET2 means DW_EH_PE_pcrel | DW_EH_PE_indirect in DWARF parlance on > Linux, but the declared TType encoding is different: > > .LLSDA0: > .byte 0xff @ @LPStart format (omit) > .byte 0 @ @TType format (absolute) > .uleb128 .LLSDATT0-.LLSDATTD0 @ @TType base offset > > i.e. it's the DW_EH_PE_absptr default. > > This works in C++ because of the _GLIBCXX_OVERRIDE_TTYPE_ENCODING kludge, > which overrides the declared encoding during the parsing of the EH table: Ok and I suspect the kludge has to continue for some more time. > > // Find @TType, the base of the handler and exception spec type data. > info->ttype_encoding = *p++; > if (info->ttype_encoding != DW_EH_PE_omit) > { > #if _GLIBCXX_OVERRIDE_TTYPE_ENCODING > /* Older ARM EABI toolchains set this value incorrectly, so use a > hardcoded OS-specific format. */ > info->ttype_encoding = _GLIBCXX_OVERRIDE_TTYPE_ENCODING; > #endif > p = read_uleb128 (p, &tmp); > info->TType = p + tmp; > } > else > info->TType = 0; > > This comes from http://gcc.gnu.org/ml/gcc-patches/2011-09/msg00765.html > > Note that the above comment suggests that Paul's intent was to fix the bogus > declared encoding in newer toolchains, but he didn't because of a misplaced > #endif as spotted by Tristan. Hence the attached patch, which aligns the > declared encoding with the actual encoding and yields the correct: > > .LLSDA0: > .byte 0xff @ @LPStart format (omit) > .byte 0x90 @ @TType format (indirect pcrel) > .uleb128 .LLSDATT0-.LLSDATTD0 @ @TType base offset > > which fixes the Ada failures in the process. It was kindly tested by Bernd > Edlinger on armv7l-unknown-linux-gnueabihf (all languages) with no regressions > so we would like to have it for 4.9.x. Ok if no regressions. Ramana > > > 2014-04-25 Douglas B Rupp <r...@adacore.com> > > PR target/60504 > * config/arm/arm.h (ASM_PREFERRED_EH_DATA_FORMAT): Expose from > ARM_TARGET2_DWARF_FORMAT. > > > > 2014-04-25 Eric Botcazou <ebotca...@adacore.com> > > * gnat.dg/test_raise_from_pure.adb: UnXFAIL for ARM. > > > -- > Eric Botcazou
