Re: [kvm-unit-tests PATCH 1/5] s390x: Add a linker script to assembly snippets

Claudio Imbrenda
2022-11-23T13:29:07Z

On Wed, 23 Nov 2022 08:46:52 +0000
Janosch Frank <frankja@linux.ibm.com> wrote:

> A linker script has a few benefits:
> - Random data doesn't end up in the binary breaking tests
> - We can easily define a lowcore and load the snippet from 0x0 instead
> of 0x4000 which makes asm snippets behave like c snippets
> - We can easily define an invalid PGM new PSW to ensure an exit on a
> guest PGM
>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

looks good in general, but I have a few questions

> ---
> lib/s390x/snippet.h | 3 +--
> s390x/Makefile | 5 +++--
> s390x/mvpg-sie.c | 2 +-
> s390x/pv-diags.c | 6 +++---
> s390x/snippets/asm/flat.lds | 43 +++++++++++++++++++++++++++++++++++++
> 5 files changed, 51 insertions(+), 8 deletions(-)
> create mode 100644 s390x/snippets/asm/flat.lds
>
> diff --git a/lib/s390x/snippet.h b/lib/s390x/snippet.h
> index b17b2a4c..57045994 100644
> --- a/lib/s390x/snippet.h
> +++ b/lib/s390x/snippet.h
> @@ -32,8 +32,7 @@
>
> #define SNIPPET_PV_TWEAK0 0x42UL
> #define SNIPPET_PV_TWEAK1 0UL
> -#define SNIPPET_OFF_C 0
> -#define SNIPPET_OFF_ASM 0x4000
> +#define SNIPPET_UNPACK_OFF 0
>
>
> /*
> diff --git a/s390x/Makefile b/s390x/Makefile
> index bf1504f9..bb0f9eb8 100644
> --- a/s390x/Makefile
> +++ b/s390x/Makefile
> @@ -135,7 +135,8 @@ $(SNIPPET_DIR)/c/%.o: $(SNIPPET_DIR)/c/%.c $(asm-offsets)
> $(CC) $(CFLAGS) -c -nostdlib -o $@ $<
>
> $(SNIPPET_DIR)/asm/%.gbin: $(SNIPPET_DIR)/asm/%.o
> - $(OBJCOPY) -O binary -j ".rodata" -j ".text" -j ".data" -j ".bss" --set-section-flags .bss=alloc,load,contents $(patsubst %.gbin,%.o,$@) $@
> + $(CC) $(LDFLAGS) -o $@ -T $(SRCDIR)/s390x/snippets/asm/flat.lds $(patsubst %.gbin,%.o,$@)

I think you can simply use $< instead of the patsubst expression

> + $(OBJCOPY) -O binary -j ".rodata" -j ".lowcore" -j ".text" -j ".data" -j ".bss" --set-section-flags .bss=alloc,load,contents $@ $@
> truncate -s '%4096' $@
>
> $(SNIPPET_DIR)/c/%.gbin: $(SNIPPET_DIR)/c/%.o $(snippet_lib) $(FLATLIBS)
> @@ -144,7 +145,7 @@ $(SNIPPET_DIR)/c/%.gbin: $(SNIPPET_DIR)/c/%.o $(snippet_lib) $(FLATLIBS)
> truncate -s '%4096' $@
>
> $(SNIPPET_DIR)/asm/%.hdr: $(SNIPPET_DIR)/asm/%.gbin $(HOST_KEY_DOCUMENT)
> - $(GEN_SE_HEADER) -k $(HOST_KEY_DOCUMENT) -c $<,0x4000,0x00000000000000420000000000000000 --psw-addr 0x4000 -o $@
> + $(GEN_SE_HEADER) -k $(HOST_KEY_DOCUMENT) -c $<,0x0,0x00000000000000420000000000000000 --psw-addr 0x4000 -o $@
>
> $(SNIPPET_DIR)/c/%.hdr: $(SNIPPET_DIR)/c/%.gbin $(HOST_KEY_DOCUMENT)
> $(GEN_SE_HEADER) -k $(HOST_KEY_DOCUMENT) -c $<,0x0,0x00000000000000420000000000000000 --psw-addr 0x4000 -o $@
> diff --git a/s390x/mvpg-sie.c b/s390x/mvpg-sie.c
> index 46a2edb6..99f4859b 100644
> --- a/s390x/mvpg-sie.c
> +++ b/s390x/mvpg-sie.c
> @@ -87,7 +87,7 @@ static void setup_guest(void)
>
> snippet_setup_guest(&vm, false);
> snippet_init(&vm, SNIPPET_NAME_START(c, mvpg_snippet),
> - SNIPPET_LEN(c, mvpg_snippet), SNIPPET_OFF_C);
> + SNIPPET_LEN(c, mvpg_snippet), SNIPPET_UNPACK_OFF);
>
> /* Enable MVPG interpretation as we want to test KVM and not ourselves */
> vm.sblk->eca = ECA_MVPGI;
> diff --git a/s390x/pv-diags.c b/s390x/pv-diags.c
> index 9ced68c7..5165937a 100644
> --- a/s390x/pv-diags.c
> +++ b/s390x/pv-diags.c
> @@ -28,7 +28,7 @@ static void test_diag_500(void)
>
> snippet_pv_init(&vm, SNIPPET_NAME_START(asm, snippet_pv_diag_500),
> SNIPPET_HDR_START(asm, snippet_pv_diag_500),
> - size_gbin, size_hdr, SNIPPET_OFF_ASM);
> + size_gbin, size_hdr, SNIPPET_UNPACK_OFF);
>
> sie(&vm);
> report(vm.sblk->icptcode == ICPT_PV_INSTR && vm.sblk->ipa == 0x8302 &&
> @@ -83,7 +83,7 @@ static void test_diag_288(void)
>
> snippet_pv_init(&vm, SNIPPET_NAME_START(asm, snippet_pv_diag_288),
> SNIPPET_HDR_START(asm, snippet_pv_diag_288),
> - size_gbin, size_hdr, SNIPPET_OFF_ASM);
> + size_gbin, size_hdr, SNIPPET_UNPACK_OFF);
>
> sie(&vm);
> report(vm.sblk->icptcode == ICPT_PV_INSTR && vm.sblk->ipa == 0x8302 &&
> @@ -124,7 +124,7 @@ static void test_diag_yield(void)
>
> snippet_pv_init(&vm, SNIPPET_NAME_START(asm, snippet_pv_diag_yield),
> SNIPPET_HDR_START(asm, snippet_pv_diag_yield),
> - size_gbin, size_hdr, SNIPPET_OFF_ASM);
> + size_gbin, size_hdr, SNIPPET_UNPACK_OFF);
>
> /* 0x44 */
> report_prefix_push("0x44");
> diff --git a/s390x/snippets/asm/flat.lds b/s390x/snippets/asm/flat.lds
> new file mode 100644
> index 00000000..366d2d78
> --- /dev/null
> +++ b/s390x/snippets/asm/flat.lds
> @@ -0,0 +1,43 @@
> +SECTIONS
> +{
> + .lowcore : {
> + /*
> + * Initial short psw for disk boot, with 31 bit addressing for
> + * non z/Arch environment compatibility and the instruction
> + * address 0x4000.
> + */
> + . = 0;
> + LONG(0x00080000)
> + LONG(0x80004000)
> + /* Restart new PSW for booting via PSW restart. */
> + . = 0x1a0;
> + QUAD(0x0000000180000000)
> + QUAD(0x0000000000004000)
> + /*
> + * Invalid PGM new PSW so we hopefully get a code 8
> + * intercept on a PGM
> + */
> + . = 0x1d0;
> + QUAD(0x0008000000000000)
> + QUAD(0x0000000000000001)
> + }
> + . = 0x4000;
> + .text : {
> + *(.text)
> + *(.text.*)
> + }
> + . = ALIGN(64K);

any reason to align to 64k? (instead of e.g. 4k)

> + etext = .;
> + . = ALIGN(16);

do you need the ALIGN? I would think we are already aligned here

> + .data : {
> + *(.data)
> + *(.data.rel*)
> + }
> + . = ALIGN(16);
> + .rodata : { *(.rodata) *(.rodata.*) }
> + . = ALIGN(16);
> + __bss_start = .;
> + .bss : { *(.bss) }
> + __bss_end = .;
> + . = ALIGN(64K);

same question as above regarding 64k

> +}