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

Janis Schoetterl-Glausch
2022-11-24T20:43:05Z

On Wed, 2022-11-23 at 08:46 +0000, Janosch Frank 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>
> ---
> 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

You could also get rid of the offset parameter, couldn't you?
>
>
> /*
> 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 $(patsubst %.gbin,%.o,$@)
> + $(OBJCOPY) -O binary -j ".rodata" -j ".lowcore" -j ".text" -j ".data" -j ".bss" --set-section-flags .bss=alloc,load,contents $@ $@

I assume .bss=alloc allocates the bss in the binary...

> 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/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);
> + etext = .;
> + . = ALIGN(16);
> + .data : {
> + *(.data)
> + *(.data.rel*)
> + }
> + . = ALIGN(16);
> + .rodata : { *(.rodata) *(.rodata.*) }
> + . = ALIGN(16);
> + __bss_start = .;

.. so the __bss symbols are not necessary.
But then, the c flat.lds has them too.
> + .bss : { *(.bss) }
> + __bss_end = .;
> + . = ALIGN(64K);
> +}