[PATCH V5] PowerPC: fix for gdb.base/eh_return.exp
will schmidt
will_schmidt@vnet.ibm.com
Wed Jun 8 16:29:08 GMT 2022
On Wed, 2022-06-08 at 08:36 -0700, Carl Love wrote:
> Will, Pedro, Kevin, GDB maintainers:
>
> Oops, accidentally hit send. Didn't get the patch attached yet.
>
> I have made the additional fixes to the comments and the setting of the
> clang options as mentioned by Will in version 4. I do not have an
> environment where gdb can be built with clang. But I did check that
> the clang options are properly passed to the compile command.
> Unfortunately, extensive testing of gdb built with XLC and clang are
> beyond the scope of this patch as I do not have access to such systems.
>
> Per the comments from Kevin, the patch was updated to check for the gcc
> and xlc compilers on PowerPC. The patch was also tested and verified
> on AIX which uses the gcc compiler to build gdb. The attempt to build
> gdb using the xlc compiler fails due to unrelated compiler errors. The
> xlc options to disable the Traceback Table was verified but that was
> it.
>
> I have updated the patch per the comments from Will. The new version
> of the patch uses a PowerPC specific gcc option to suppress the
> generation of the Traceback Table information. The Traceback
> information for this function is contained in the .long statements
> following the last instruction in the function. The Traceback table
> consists of a series of bit fields. The assembler tries to interpret
> the Traceback Table as instructions. If the bits in the Traceback
> Table happen to match a known instruction, the assembler will print a
> bogus instruction, otherwise the assembler just prints the bits using
> the .long statement. Unfortunately, the disassembler does not know how
> to locate the Traceback Table information at the end of a function.
>
> With this patch, the Traceback Table is disabled, so the last
> instruction of the function is accurately found. Previously, the break
> point was set at the last .long statement which gdb will never reach.
> The test now passes as gdb successfully executes to the identified last
> instruction.
>
> Note, the use of the gcc mtraceback option is not valid on other
> architectures.
>
> I have tested the patch on Linux Power 10 with gcc, AIX with the gcc
> and Intel with gcc.
>
> Please let me know if this patch is acceptable. Thanks for the input
> and help with the patch.
>
> Carl Love
>
> ------------------------------------------------------------------
>
> PowerPC: fix for gdb.base/eh_return.exp
>
> Disable the Traceback Table generation on PowerPC for this test. The
> Traceback Table consists of a series of bit fields to indicate things like
> the Traceback Table version, language, and specific information about the
> function. The Traceback Table is generated following the end of the code
> for every function by default. The Traceback Table is defined in the
> PowerPC ELF ABI and is intended to support debuggers and exception
> handlers. The Traceback Table is displayed in the disassembly of functions
> by default and is part of the function length. The table is typically
> interpreted by the disassembler as data represented by .long xxx entries.
>
> Generation of the Traceback Table is disabled in this test using the
> PowerPC specific gcc compiler option -mtraceback=no, the xlc option
> additional_flags-qtable=none and the clang optons
> -mllvm -xcoff-traceback-table=false. Disabling the Traceback Table
> generation in this test results in the gdb_test_multiple statement
> correctly locating the address of the bclr instruction before the statement
> "End of assembler dump." in the disassembly output.
> ---
> gdb/testsuite/gdb.base/eh_return.exp | 36 +++++++++++++++++++++++++++-
> 1 file changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/gdb/testsuite/gdb.base/eh_return.exp b/gdb/testsuite/gdb.base/eh_return.exp
> index df55dbc72da..6e4b9bd0bba 100644
> --- a/gdb/testsuite/gdb.base/eh_return.exp
> +++ b/gdb/testsuite/gdb.base/eh_return.exp
> @@ -18,8 +18,42 @@
>
> standard_testfile
>
> +# Set compiler flags.
> +if {[istarget "powerpc*"]} then {
> + # PowerPC generates a Traceback Table, as defined in the PPC64 ABI,
> + # following each function by default. The Traceback Table information is
> + # typically interpreted by the disassembler as data represented with
> + # .long xxxx following the last instruction in the function. For example:
> + #
> + # Dump of assembler code for function eh2:
> + # 0x00000000100009e0 <+0>: lis r2,4098
> + # ...
> + # 0x0000000010000b04 <+292>: add r1,r1,r10
> + # 0x0000000010000b08 <+296>: blr
> + # 0x0000000010000b0c <+300>: .long 0x0
> + # 0x0000000010000b10 <+304>: .long 0x1000000
> + # 0x0000000010000b14 <+308>: .long 0x1000180
> + # End of assembler dump.
> + #
> + # Disable the Traceback Table generation, using the PowerPC specific
> + # compiler option, so the test gdb_test_multiple "disassemble eh2" will
> + # locate the address of the blr instruction not the last .long statement.
> + if { [test_compiler_info "gcc-*"] } {
> + set compile_flags {debug nopie additional_flags=-mtraceback=no}
> + } elseif { [test_compiler_info "xlc-*"] } {
> + set compile_flags {debug nopie additional_flags=-qtbtable=none}
> + } elseif { [test_compiler_info "clang-*"] } {
> + set compile_flags [list debug nopie additional_flags=-mllvm \
> + additional_flags=-xcoff-traceback-table=false]
> + } else {
> + set compile_flags {debug nopie }
> + }
> +} else {
> + set compile_flags {debug nopie}
> +}
> +
> if {[prepare_for_testing "failed to prepare" $testfile $srcfile \
> - {debug nopie}]} {
> + $compile_flags]} {
> return -1
> }
This looks good to me. Thanks for the multiple iterations and updates.
I am not an approver but I recommend approval. :-)
Thanks
-Will
>
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