Ping?
On Thu, 14 May 2020 at 16:57, Christophe Lyon
<christophe.l...@linaro.org> wrote:
>
> The interrupt attribute does not guarantee that the FP registers are
> saved, which can result in problems difficult to debug.
>
> Saving the FP registers and status registers can be a large penalty,
> so it's probably not desirable to do that all the time.
>
> If the handler calls other functions, we'd likely need to save all of
> them, for lack of knowledge of which registers they actually clobber.
>
> This is even more obscure for the end-user when the compiler inserts
> calls to helper functions such as memcpy (some multilibs do use FP
> registers to speed it up).
>
> In the PR, we discussed adding routines in libgcc to save the FP
> context and saving only locally-clobbered FP registers, but this seems
> to be too much work for the purpose, given that in general such
> handlers try to avoid this kind of penalty.
> I suspect we would also want new attributes to instruct the compiler
> that saving the FP context is not needed.
>
> In the mean time, emit a warning to suggest re-compiling with
> -mgeneral-regs-only. Note that this can lead to errors if the code
> uses floating-point and -mfloat-abi=hard, eg:
> argument of type 'double' not permitted with -mgeneral-regs-only
>
> This can be troublesome for the user, but at least this would make
> him aware of the latent issue.
>
> The patch adds several testcases:
>
> - pr94734-1-hard.c checks that a warning is emitted when using
> -mfloat-abi=hard. Function IRQ_HDLR_Test can make implicit calls to
> runtime floating-point routines (or direct use of FP instructions),
> IRQ_HDLR_Test2 doesn't. We emit a warning in both cases, though.
>
> - pr94734-1-softfp.c: same as above wih -mfloat-abi=softfp.
>
> - pr94734-1-soft.c checks that no warning is emitted when using
> -mfloat-abi=soft when the same code as above.
>
> - pr94734-2.c checks that no warning is emitted when using
> -mgeneral-regs-only.
>
> - pr94734-3.c checks that no warning is emitted when using
> -mgeneral-regs-only even using float-point data.
>
> 2020-05-14 Christophe Lyon <christophe.l...@linaro.org>
>
> PR target/94743
> gcc/
> * config/arm/arm.c (arm_handle_isr_attribute): Warn if
> -mgeneral-regs-only is not used.
>
> gcc/testsuite/
> * gcc.misc-tests/arm-isr.c: Add -mgeneral-regs-only.
> * gcc.target/arm/empty_fiq_handler.c: Add -mgeneral-regs-only.
> * gcc.target/arm/interrupt-1.c: Add -mgeneral-regs-only.
> * gcc.target/arm/interrupt-2.c: Add -mgeneral-regs-only.
> * gcc.target/arm/pr70830.c: Add -mgeneral-regs-only.
> * gcc.target/arm/pr94743-1-hard.c: New test.
> * gcc.target/arm/pr94743-1-soft.c: New test.
> * gcc.target/arm/pr94743-1-softfp.c: New test.
> * gcc.target/arm/pr94743-2.c: New test.
> * gcc.target/arm/pr94743-3.c: New test.
> ---
> gcc/config/arm/arm.c | 5 ++++
> gcc/testsuite/gcc.misc-tests/arm-isr.c | 2 ++
> gcc/testsuite/gcc.target/arm/empty_fiq_handler.c | 1 +
> gcc/testsuite/gcc.target/arm/interrupt-1.c | 2 +-
> gcc/testsuite/gcc.target/arm/interrupt-2.c | 2 +-
> gcc/testsuite/gcc.target/arm/pr70830.c | 2 +-
> gcc/testsuite/gcc.target/arm/pr94743-1-hard.c | 29
> ++++++++++++++++++++++++
> gcc/testsuite/gcc.target/arm/pr94743-1-soft.c | 27 ++++++++++++++++++++++
> gcc/testsuite/gcc.target/arm/pr94743-1-softfp.c | 29
> ++++++++++++++++++++++++
> gcc/testsuite/gcc.target/arm/pr94743-2.c | 22 ++++++++++++++++++
> gcc/testsuite/gcc.target/arm/pr94743-3.c | 23 +++++++++++++++++++
> 11 files changed, 141 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/arm/pr94743-1-hard.c
> create mode 100644 gcc/testsuite/gcc.target/arm/pr94743-1-soft.c
> create mode 100644 gcc/testsuite/gcc.target/arm/pr94743-1-softfp.c
> create mode 100644 gcc/testsuite/gcc.target/arm/pr94743-2.c
> create mode 100644 gcc/testsuite/gcc.target/arm/pr94743-3.c
>
> diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
> index dda8771..c88de3e 100644
> --- a/gcc/config/arm/arm.c
> +++ b/gcc/config/arm/arm.c
> @@ -7232,6 +7232,11 @@ arm_handle_isr_attribute (tree *node, tree name, tree
> args, int flags,
> name);
> *no_add_attrs = true;
> }
> + else if (TARGET_VFP_BASE)
> + {
> + warning (OPT_Wattributes, "FP registers might be clobbered despite
> %qE attribute: compile with -mgeneral-regs-only",
> + name);
> + }
> /* FIXME: the argument if any is checked for type attributes;
> should it be checked for decl ones? */
> }
> diff --git a/gcc/testsuite/gcc.misc-tests/arm-isr.c
> b/gcc/testsuite/gcc.misc-tests/arm-isr.c
> index 737f9ff..9eff52c 100644
> --- a/gcc/testsuite/gcc.misc-tests/arm-isr.c
> +++ b/gcc/testsuite/gcc.misc-tests/arm-isr.c
> @@ -1,3 +1,5 @@
> +/* { dg-options "-mgeneral-regs-only" } */
> +
> extern void abort ();
> extern void exit (int);
>
> diff --git a/gcc/testsuite/gcc.target/arm/empty_fiq_handler.c
> b/gcc/testsuite/gcc.target/arm/empty_fiq_handler.c
> index 8313f21..6911ffc 100644
> --- a/gcc/testsuite/gcc.target/arm/empty_fiq_handler.c
> +++ b/gcc/testsuite/gcc.target/arm/empty_fiq_handler.c
> @@ -1,5 +1,6 @@
> /* { dg-do compile } */
> /* { dg-skip-if "" { ! arm_cortex_m } { "-mthumb" } } */
> +/* { dg-options "-mgeneral-regs-only" } */
>
> /* Below code used to trigger an ICE due to missing constraints for
> sp = fp + cst pattern. */
> diff --git a/gcc/testsuite/gcc.target/arm/interrupt-1.c
> b/gcc/testsuite/gcc.target/arm/interrupt-1.c
> index 493763d..de1ecc5 100644
> --- a/gcc/testsuite/gcc.target/arm/interrupt-1.c
> +++ b/gcc/testsuite/gcc.target/arm/interrupt-1.c
> @@ -2,7 +2,7 @@
> __attribute__ ((interrupt)). */
> /* { dg-do assemble } */
> /* { dg-require-effective-target arm_nothumb } */
> -/* { dg-options "-O0 -marm -save-temps" } */
> +/* { dg-options "-mgeneral-regs-only -O0 -marm -save-temps" } */
>
> /* This test is not valid when -mthumb. */
> extern void bar (int);
> diff --git a/gcc/testsuite/gcc.target/arm/interrupt-2.c
> b/gcc/testsuite/gcc.target/arm/interrupt-2.c
> index 5be1f16..c64b98b 100644
> --- a/gcc/testsuite/gcc.target/arm/interrupt-2.c
> +++ b/gcc/testsuite/gcc.target/arm/interrupt-2.c
> @@ -2,7 +2,7 @@
> __attribute__ ((interrupt)). */
> /* { dg-do assemble } */
> /* { dg-require-effective-target arm_nothumb } */
> -/* { dg-options "-O1 -marm -save-temps" } */
> +/* { dg-options "-mgeneral-regs-only -O1 -marm -save-temps" } */
>
> /* This test is not valid when -mthumb. */
> extern void bar (int);
> diff --git a/gcc/testsuite/gcc.target/arm/pr70830.c
> b/gcc/testsuite/gcc.target/arm/pr70830.c
> index cd84c42..bca596c 100644
> --- a/gcc/testsuite/gcc.target/arm/pr70830.c
> +++ b/gcc/testsuite/gcc.target/arm/pr70830.c
> @@ -1,7 +1,7 @@
> /* PR target/70830. */
> /* { dg-do assemble } */
> /* { dg-require-effective-target arm_arm_ok } */
> -/* { dg-options "-Os -marm -save-temps" } */
> +/* { dg-options "-mgeneral-regs-only -Os -marm -save-temps" } */
>
> /* This test is not valid when -mthumb. */
>
> diff --git a/gcc/testsuite/gcc.target/arm/pr94743-1-hard.c
> b/gcc/testsuite/gcc.target/arm/pr94743-1-hard.c
> new file mode 100644
> index 0000000..928b79d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/pr94743-1-hard.c
> @@ -0,0 +1,29 @@
> +/* PR target/94743 */
> +/* { dg-do compile } */
> +/* { dg-skip-if "do not override -mfloat-abi" { *-*-* } { "-mfloat-abi=*" }
> {"-mfloat-abi=hard" } } */
> +/* { dg-require-effective-target arm_vfp_ok } */
> +/* { dg-add-options arm_vfp } */
> +/* Make sure with use -mfloat-abi=hard. */
> +/* { dg-additional-options "-mfloat-abi=hard" } */
> +
> +/* Check that we emit a warning when compiling an IRQ handler without
> + -mgeneral-regs-only. */
> +typedef struct {
> + double fpdata[32];
> +} dummy_t;
> +
> +dummy_t global_d;
> +dummy_t global_d1;
> +
> +/* This function may clobber VFP registers. */
> +__attribute__ ((interrupt("IRQ"))) void IRQ_HDLR_Test(void)
> +{ /* { dg-warning { FP registers might be clobbered despite 'interrupt'
> attribute: compile with -mgeneral-regs-only} "" { target *-*-* } . } */
> + global_d.fpdata[3] += global_d.fpdata[3] * global_d1.fpdata[3];
> +}
> +
> +/* This function does not need to clobber VFP registers. */
> +/* Do we want to emit a (useless?) warning? */
> +__attribute__ ((interrupt("IRQ"))) void IRQ_HDLR_Test2(void)
> +{ /* { dg-warning { FP registers might be clobbered despite 'interrupt'
> attribute: compile with -mgeneral-regs-only} "" { target *-*-* } . } */
> + global_d.fpdata[3] = 1.0;
> +}
> diff --git a/gcc/testsuite/gcc.target/arm/pr94743-1-soft.c
> b/gcc/testsuite/gcc.target/arm/pr94743-1-soft.c
> new file mode 100644
> index 0000000..e06a16d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/pr94743-1-soft.c
> @@ -0,0 +1,27 @@
> +/* PR target/94743 */
> +/* { dg-do compile } */
> +/* Thumb1 mode not supported for interrupt routines. */
> +/* { dg-require-effective-target arm32 } */
> +/* { dg-skip-if "do not override -mfloat-abi" { *-*-* } { "-mfloat-abi=*" }
> {"-mfloat-abi=soft" } } */
> +/* { dg-options "-mfloat-abi=soft" } */
> +
> +/* Check that we do not emit a warning when compiling an IRQ handler without
> + -mgeneral-regs-only with -mfloat-abi=soft. */
> +typedef struct {
> + double fpdata[32];
> +} dummy_t;
> +
> +dummy_t global_d;
> +dummy_t global_d1;
> +
> +/* This function may clobber VFP registers. */
> +__attribute__ ((interrupt("IRQ"))) void IRQ_HDLR_Test(void)
> +{
> + global_d.fpdata[3] += global_d.fpdata[3] * global_d1.fpdata[3];
> +}
> +
> +/* This function does not need to clobber VFP registers. */
> +__attribute__ ((interrupt("IRQ"))) void IRQ_HDLR_Test2(void)
> +{
> + global_d.fpdata[3] = 1.0;
> +}
> diff --git a/gcc/testsuite/gcc.target/arm/pr94743-1-softfp.c
> b/gcc/testsuite/gcc.target/arm/pr94743-1-softfp.c
> new file mode 100644
> index 0000000..6113eb6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/pr94743-1-softfp.c
> @@ -0,0 +1,29 @@
> +/* PR target/94743 */
> +/* { dg-do compile } */
> +/* { dg-skip-if "do not override -mfloat-abi" { *-*-* } { "-mfloat-abi=*" }
> {"-mfloat-abi=softfp" } } */
> +/* { dg-require-effective-target arm_vfp_ok } */
> +/* { dg-add-options arm_vfp } */
> +/* Make sure with use -mfloat-abi=softfp. */
> +/* { dg-additional-options "-mfloat-abi=softfp" } */
> +
> +/* Check that we emit a warning when compiling an IRQ handler without
> + -mgeneral-regs-only. */
> +typedef struct {
> + double fpdata[32];
> +} dummy_t;
> +
> +dummy_t global_d;
> +dummy_t global_d1;
> +
> +/* This function may clobber VFP registers. */
> +__attribute__ ((interrupt("IRQ"))) void IRQ_HDLR_Test(void)
> +{ /* { dg-warning { FP registers might be clobbered despite 'interrupt'
> attribute: compile with -mgeneral-regs-only} "" { target *-*-* } . } */
> + global_d.fpdata[3] += global_d.fpdata[3] * global_d1.fpdata[3];
> +}
> +
> +/* This function does not need to clobber VFP registers. */
> +/* Do we want to emit a (useless?) warning? */
> +__attribute__ ((interrupt("IRQ"))) void IRQ_HDLR_Test2(void)
> +{ /* { dg-warning { FP registers might be clobbered despite 'interrupt'
> attribute: compile with -mgeneral-regs-only} "" { target *-*-* } . } */
> + global_d.fpdata[3] = 1.0;
> +}
> diff --git a/gcc/testsuite/gcc.target/arm/pr94743-2.c
> b/gcc/testsuite/gcc.target/arm/pr94743-2.c
> new file mode 100644
> index 0000000..50a97de
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/pr94743-2.c
> @@ -0,0 +1,22 @@
> +/* PR target/94743 */
> +/* { dg-do compile } */
> +/* Thumb1 mode not supported for interrupt routines. */
> +/* { dg-require-effective-target arm32 } */
> +/* { dg-options "-mgeneral-regs-only" } */
> +
> +/* Check that we do not emit a warning when compiling an IRQ handler
> + with -mgeneral-regs-only. */
> +typedef struct {
> + /* Do not use floating-point types, which are not compatible with
> + -mgeneral-regs-only under -mfloat-abi=hard */
> + int fpdata[32];
> +} dummy_t;
> +
> +dummy_t global_d;
> +dummy_t global_d1;
> +
> +/* This function does not clobber VFP registers. */
> +__attribute__ ((interrupt("IRQ"))) void IRQ_HDLR_Test(void)
> +{
> + global_d.fpdata[3] += global_d.fpdata[3] * global_d1.fpdata[3];
> +}
> diff --git a/gcc/testsuite/gcc.target/arm/pr94743-3.c
> b/gcc/testsuite/gcc.target/arm/pr94743-3.c
> new file mode 100644
> index 0000000..6b8ed2b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/pr94743-3.c
> @@ -0,0 +1,23 @@
> +/* PR target/94743 */
> +/* { dg-do compile } */
> +/* Thumb1 mode not supported for interrupt routines. */
> +/* { dg-require-effective-target arm32 } */
> +/* { dg-skip-if "do not override -mfloat-abi" { *-*-* } { "-mfloat-abi=*" }
> {"-mfloat-abi=soft" } } */
> +/* { dg-options "-mgeneral-regs-only -mfloat-abi=soft" } */
> +
> +/* Check that we do not emit a warning when compiling an IRQ handler
> + with -mgeneral-regs-only even when using floating-point data. */
> +typedef struct {
> + /* Since we use -mfloat=abi=soft, this will generate calls to
> + libgcc, but won't clobber VFP registers. */
> + double fpdata[32];
> +} dummy_t;
> +
> +dummy_t global_d;
> +dummy_t global_d1;
> +
> +/* This function does not clobber VFP registers. */
> +__attribute__ ((interrupt("IRQ"))) void IRQ_HDLR_Test(void)
> +{
> + global_d.fpdata[3] += global_d.fpdata[3] * global_d1.fpdata[3];
> +}
> --
> 2.7.4
>
