| Message ID | 000001cef10a$a35819b0$ea084d10$@bolton@arm.com |
|---|---|
| State | New |
| Headers | show |
On Wed, 4 Dec 2013, Ian Bolton wrote: > The main update, other than cosmetic differences, is that we've chosen > the same ARM encoding as LLVM for practical purposes. (The Thumb > encoding in Mark's patch already matched LLVM.) Do the encodings match what plain "udf" does in recent-enough gas (too recent for us to assume it in GCC or glibc for now), or is it something else?
> On Wed, 4 Dec 2013, Ian Bolton wrote: > > > The main update, other than cosmetic differences, is that we've > chosen > > the same ARM encoding as LLVM for practical purposes. (The Thumb > > encoding in Mark's patch already matched LLVM.) > > Do the encodings match what plain "udf" does in recent-enough gas (too > recent for us to assume it in GCC or glibc for now), or is it something > else? Hi Joseph, Yes, these encodings match the UDF instruction that is defined in the most recent edition of the ARM architecture reference manual. Thumb: 0xde00 | imm8 (we chose 0xff for the imm8) ARM: 0xe7f000f0 | (imm12 << 8) | imm4 (we chose to use 0 for both imms) So as not to break old versions of gas that don't recognise UDF, the encoding is output directly. Apologies if I have over-explained there! Cheers, Ian
On 04/12/13 16:05, Ian Bolton wrote: > Hi, > > Currently, on ARM, you have to either call abort() or raise(SIGTRAP) > to achieve a handy crash. > > This patch allows you to instead call __builtin_trap() which is much > more efficient at falling over because it becomes just a single > instruction that will trap for you. > > Two testcases have been added (for ARM and Thumb) and both pass. > > > Note: This is a modified version of a patch originally submitted by Mark > Mitchell back in 2010, which came in response to PR target/59091. The PR came as a result of the A64 implementation of __builtin_trap. The original patch was much earlier than that :) > > http://gcc.gnu.org/ml/gcc-patches/2010-09/msg00639.html > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59091 > > The main update, other than cosmetic differences, is that we've chosen > the same ARM encoding as LLVM for practical purposes. (The Thumb > encoding in Mark's patch already matched LLVM.) > > > OK for trunk? This is OK for trunk. Please put the PR numbers in the changelog entries before committing i.e. PR target/59091. FTR, these match with the encodings for the udf mnemonic with an immediate value of 0 in ARM state and #0xff in Thumb state. Obviously we cannot put out the udf mnemonic out because an older gas will not support it. These immediates were chosen to match the values as in other compiler implementations (I know these match with LLVM as something I can point to externally) and have been double checked with folks who have an avid interest in the kernel world. Thanks, Ramana
On 4 Dec 2013, at 16:08, "Ian Bolton" <ian.bolton@arm.com> wrote: > Hi, > > Currently, on ARM, you have to either call abort() or raise(SIGTRAP) > to achieve a handy crash. > > This patch allows you to instead call __builtin_trap() which is much > more efficient at falling over because it becomes just a single > instruction that will trap for you. > > Two testcases have been added (for ARM and Thumb) and both pass. > > > Note: This is a modified version of a patch originally submitted by Mark > Mitchell back in 2010, which came in response to PR target/59091. > > http://gcc.gnu.org/ml/gcc-patches/2010-09/msg00639.html > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59091 > > The main update, other than cosmetic differences, is that we've chosen > the same ARM encoding as LLVM for practical purposes. (The Thumb > encoding in Mark's patch already matched LLVM.) > > > OK for trunk? > > Cheers, > Ian > > > 2013-12-04 Ian Bolton <ian.bolton@arm.com> > Mark Mitchell <mark@codesourcery.com> > > gcc/ > * config/arm/arm.md (trap): New pattern. > * config/arm/types.md: Added a type for trap. > > testsuite/ > * gcc.target/arm/builtin-trap.c: New test. > * gcc.target/arm/thumb-builtin-trap.c: Likewise. > <aarch32-builtin-trap-v2.txt> This needs to set the conds attribute to "unconditional". Otherwise the ARM backend might try to turn this into a conditional instruction. R.
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md index dd73366..3b7a827 100644 --- a/gcc/config/arm/arm.md +++ b/gcc/config/arm/arm.md @@ -9927,6 +9927,22 @@ (set_attr "type" "mov_reg")] ) +(define_insn "trap" + [(trap_if (const_int 1) (const_int 0))] + "" + "* + if (TARGET_ARM) + return \".inst\\t0xe7f000f0\"; + else + return \".inst\\t0xdeff\"; + " + [(set (attr "length") + (if_then_else (eq_attr "is_thumb" "yes") + (const_int 2) + (const_int 4))) + (set_attr "type" "trap")] +) + ;; Patterns to allow combination of arithmetic, cond code and shifts diff --git a/gcc/config/arm/types.md b/gcc/config/arm/types.md index 1c4b9e3..6351f08 100644 --- a/gcc/config/arm/types.md +++ b/gcc/config/arm/types.md @@ -152,6 +152,7 @@ ; store2 store 2 words to memory from arm registers. ; store3 store 3 words to memory from arm registers. ; store4 store 4 (or more) words to memory from arm registers. +; trap cause a trap in the kernel. ; udiv unsigned division. ; umaal unsigned multiply accumulate accumulate long. ; umlal unsigned multiply accumulate long. @@ -645,6 +646,7 @@ store2,\ store3,\ store4,\ + trap,\ udiv,\ umaal,\ umlal,\ diff --git a/gcc/testsuite/gcc.target/arm/builtin-trap.c b/gcc/testsuite/gcc.target/arm/builtin-trap.c new file mode 100644 index 0000000..4ff8d25 --- /dev/null +++ b/gcc/testsuite/gcc.target/arm/builtin-trap.c @@ -0,0 +1,10 @@ +/* { dg-do compile } */ +/* { dg-require-effective-target arm32 } */ + +void +trap () +{ + __builtin_trap (); +} + +/* { dg-final { scan-assembler "0xe7f000f0" { target { arm_nothumb } } } } */ diff --git a/gcc/testsuite/gcc.target/arm/thumb-builtin-trap.c b/gcc/testsuite/gcc.target/arm/thumb-builtin-trap.c new file mode 100644 index 0000000..22e90e7 --- /dev/null +++ b/gcc/testsuite/gcc.target/arm/thumb-builtin-trap.c @@ -0,0 +1,11 @@ +/* { dg-do compile } */ +/* { dg-options "-mthumb" } */ +/* { dg-require-effective-target arm_thumb1_ok } */ + +void +trap () +{ + __builtin_trap (); +} + +/* { dg-final { scan-assembler "0xdeff" } } */
Hi, Currently, on ARM, you have to either call abort() or raise(SIGTRAP) to achieve a handy crash. This patch allows you to instead call __builtin_trap() which is much more efficient at falling over because it becomes just a single instruction that will trap for you. Two testcases have been added (for ARM and Thumb) and both pass. Note: This is a modified version of a patch originally submitted by Mark Mitchell back in 2010, which came in response to PR target/59091. http://gcc.gnu.org/ml/gcc-patches/2010-09/msg00639.html http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59091 The main update, other than cosmetic differences, is that we've chosen the same ARM encoding as LLVM for practical purposes. (The Thumb encoding in Mark's patch already matched LLVM.) OK for trunk? Cheers, Ian 2013-12-04 Ian Bolton <ian.bolton@arm.com> Mark Mitchell <mark@codesourcery.com> gcc/ * config/arm/arm.md (trap): New pattern. * config/arm/types.md: Added a type for trap. testsuite/ * gcc.target/arm/builtin-trap.c: New test. * gcc.target/arm/thumb-builtin-trap.c: Likewise.