[PATCH 0/2] arch_dump: fix prstatus pid on s390x and ppc

[PATCH 0/2] arch_dump: fix prstatus pid on s390x and ppc

[Omar Sandoval]

Hello,

I maintain drgn [1], a debugger for the Linux kernel. I ran into a quirk
of the NT_PRSTATUS note in kernel core dumps [2], so I looked into how
QEMU's dump-guest-memory command generates NT_PRSTATUS. I noticed that
on most architectures, the note's PID field is set to the CPU ID plus 1.
There are two exceptions: on s390x, there's an endianness bug (it's not
byte swapped if the host is little endian), and on ppc, it's not set at
all (it defaults to zero). They're both easy fixes.

Thanks,
Omar

1: https://github.com/osandov/drgn
2: https://github.com/osandov/drgn/issues/404

Omar Sandoval (2):
  target/s390x/arch_dump: use correct byte order for pid
  target/ppc/arch_dump: set prstatus pid to cpuid

 target/ppc/arch_dump.c   | 21 ++++++++++++---------
 target/s390x/arch_dump.c |  2 +-
 2 files changed, 13 insertions(+), 10 deletions(-)

-- 
2.45.2

[PATCH 1/2] target/s390x/arch_dump: use correct byte order for pid

[Omar Sandoval]

The pid field of prstatus needs to be big endian like all of the other
fields.

Fixes: f738f296eaae ("s390x/arch_dump: pass cpuid into notes sections")
Signed-off-by: Omar Sandoval <osandov@osandov.com>
---
 target/s390x/arch_dump.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/s390x/arch_dump.c b/target/s390x/arch_dump.c
index 7e8a1b4fc0..029d91d93a 100644
--- a/target/s390x/arch_dump.c
+++ b/target/s390x/arch_dump.c
@@ -102,7 +102,7 @@ static void s390x_write_elf64_prstatus(Note *note, S390CPU *cpu, int id)
         regs->acrs[i] = cpu_to_be32(cpu->env.aregs[i]);
         regs->gprs[i] = cpu_to_be64(cpu->env.regs[i]);
     }
-    note->contents.prstatus.pid = id;
+    note->contents.prstatus.pid = cpu_to_be32(id);
 }
 
 static void s390x_write_elf64_fpregset(Note *note, S390CPU *cpu, int id)
-- 
2.45.2

[PATCH 2/2] target/ppc/arch_dump: set prstatus pid to cpuid

[Omar Sandoval]

Every other architecture does this, and debuggers need it to be able to
identify which prstatus note corresponds to which CPU.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
---
 target/ppc/arch_dump.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/target/ppc/arch_dump.c b/target/ppc/arch_dump.c
index a8315659d9..78b4205319 100644
--- a/target/ppc/arch_dump.c
+++ b/target/ppc/arch_dump.c
@@ -47,9 +47,11 @@ struct PPCUserRegStruct {
 } QEMU_PACKED;
 
 struct PPCElfPrstatus {
-    char pad1[112];
+    char pad1[32];
+    uint32_t pid;
+    uint8_t pad2[76];
     struct PPCUserRegStruct pr_reg;
-    char pad2[40];
+    char pad3[40];
 } QEMU_PACKED;
 
 
@@ -96,7 +98,7 @@ typedef struct NoteFuncArg {
     DumpState *state;
 } NoteFuncArg;
 
-static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
+static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
 {
     int i;
     reg_t cr;
@@ -109,6 +111,7 @@ static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
 
     prstatus = &note->contents.prstatus;
     memset(prstatus, 0, sizeof(*prstatus));
+    prstatus->pid = cpu_to_dump32(s, id);
     reg = &prstatus->pr_reg;
 
     for (i = 0; i < 32; i++) {
@@ -127,7 +130,7 @@ static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
     reg->ccr = cpu_to_dump_reg(s, cr);
 }
 
-static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu)
+static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
 {
     int i;
     struct PPCElfFpregset  *fpregset;
@@ -146,7 +149,7 @@ static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu)
     fpregset->fpscr = cpu_to_dump_reg(s, cpu->env.fpscr);
 }
 
-static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
+static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
 {
     int i;
     struct PPCElfVmxregset *vmxregset;
@@ -178,7 +181,7 @@ static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
     vmxregset->vscr.u32[3] = cpu_to_dump32(s, ppc_get_vscr(&cpu->env));
 }
 
-static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
+static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
 {
     int i;
     struct PPCElfVsxregset *vsxregset;
@@ -195,7 +198,7 @@ static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
     }
 }
 
-static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu)
+static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
 {
     struct PPCElfSperegset *speregset;
     Note *note = &arg->note;
@@ -211,7 +214,7 @@ static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu)
 
 static const struct NoteFuncDescStruct {
     int contents_size;
-    void (*note_contents_func)(NoteFuncArg *arg, PowerPCCPU *cpu);
+    void (*note_contents_func)(NoteFuncArg *arg, PowerPCCPU *cpu, int id);
 } note_func[] = {
     {sizeof_field(Note, contents.prstatus),  ppc_write_elf_prstatus},
     {sizeof_field(Note, contents.fpregset),  ppc_write_elf_fpregset},
@@ -282,7 +285,7 @@ static int ppc_write_all_elf_notes(const char *note_name,
         arg.note.hdr.n_descsz = cpu_to_dump32(s, nf->contents_size);
         strncpy(arg.note.name, note_name, sizeof(arg.note.name));
 
-        (*nf->note_contents_func)(&arg, cpu);
+        (*nf->note_contents_func)(&arg, cpu, id);
 
         note_size =
             sizeof(arg.note) - sizeof(arg.note.contents) + nf->contents_size;
-- 
2.45.2

Re: [PATCH 1/2] target/s390x/arch_dump: use correct byte order for pid

[Thomas Huth]

On 19/06/2024 07.00, Omar Sandoval wrote:
> The pid field of prstatus needs to be big endian like all of the other
> fields.
> 
> Fixes: f738f296eaae ("s390x/arch_dump: pass cpuid into notes sections")
> Signed-off-by: Omar Sandoval <osandov@osandov.com>
> ---
>   target/s390x/arch_dump.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/s390x/arch_dump.c b/target/s390x/arch_dump.c
> index 7e8a1b4fc0..029d91d93a 100644
> --- a/target/s390x/arch_dump.c
> +++ b/target/s390x/arch_dump.c
> @@ -102,7 +102,7 @@ static void s390x_write_elf64_prstatus(Note *note, S390CPU *cpu, int id)
>           regs->acrs[i] = cpu_to_be32(cpu->env.aregs[i]);
>           regs->gprs[i] = cpu_to_be64(cpu->env.regs[i]);
>       }
> -    note->contents.prstatus.pid = id;
> +    note->contents.prstatus.pid = cpu_to_be32(id);
>   }
>   
>   static void s390x_write_elf64_fpregset(Note *note, S390CPU *cpu, int id)

Reviewed-by: Thomas Huth <thuth@redhat.com>

Re: [PATCH 2/2] target/ppc/arch_dump: set prstatus pid to cpuid

[Thomas Huth]

On 19/06/2024 07.00, Omar Sandoval wrote:
> Every other architecture does this, and debuggers need it to be able to
> identify which prstatus note corresponds to which CPU.
> 
> Signed-off-by: Omar Sandoval <osandov@osandov.com>
> ---
>   target/ppc/arch_dump.c | 21 ++++++++++++---------
>   1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/target/ppc/arch_dump.c b/target/ppc/arch_dump.c
> index a8315659d9..78b4205319 100644
> --- a/target/ppc/arch_dump.c
> +++ b/target/ppc/arch_dump.c
> @@ -47,9 +47,11 @@ struct PPCUserRegStruct {
>   } QEMU_PACKED;
>   
>   struct PPCElfPrstatus {
> -    char pad1[112];
> +    char pad1[32];
> +    uint32_t pid;
> +    uint8_t pad2[76];
>       struct PPCUserRegStruct pr_reg;
> -    char pad2[40];
> +    char pad3[40];
>   } QEMU_PACKED;
>   
>   
> @@ -96,7 +98,7 @@ typedef struct NoteFuncArg {
>       DumpState *state;
>   } NoteFuncArg;
>   
> -static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       int i;
>       reg_t cr;
> @@ -109,6 +111,7 @@ static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
>   
>       prstatus = &note->contents.prstatus;
>       memset(prstatus, 0, sizeof(*prstatus));
> +    prstatus->pid = cpu_to_dump32(s, id);
>       reg = &prstatus->pr_reg;
>   
>       for (i = 0; i < 32; i++) {
> @@ -127,7 +130,7 @@ static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
>       reg->ccr = cpu_to_dump_reg(s, cr);
>   }
>   
> -static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       int i;
>       struct PPCElfFpregset  *fpregset;
> @@ -146,7 +149,7 @@ static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu)
>       fpregset->fpscr = cpu_to_dump_reg(s, cpu->env.fpscr);
>   }
>   
> -static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       int i;
>       struct PPCElfVmxregset *vmxregset;
> @@ -178,7 +181,7 @@ static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
>       vmxregset->vscr.u32[3] = cpu_to_dump32(s, ppc_get_vscr(&cpu->env));
>   }
>   
> -static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       int i;
>       struct PPCElfVsxregset *vsxregset;
> @@ -195,7 +198,7 @@ static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
>       }
>   }
>   
> -static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       struct PPCElfSperegset *speregset;
>       Note *note = &arg->note;
> @@ -211,7 +214,7 @@ static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu)
>   
>   static const struct NoteFuncDescStruct {
>       int contents_size;
> -    void (*note_contents_func)(NoteFuncArg *arg, PowerPCCPU *cpu);
> +    void (*note_contents_func)(NoteFuncArg *arg, PowerPCCPU *cpu, int id);
>   } note_func[] = {
>       {sizeof_field(Note, contents.prstatus),  ppc_write_elf_prstatus},
>       {sizeof_field(Note, contents.fpregset),  ppc_write_elf_fpregset},
> @@ -282,7 +285,7 @@ static int ppc_write_all_elf_notes(const char *note_name,
>           arg.note.hdr.n_descsz = cpu_to_dump32(s, nf->contents_size);
>           strncpy(arg.note.name, note_name, sizeof(arg.note.name));
>   
> -        (*nf->note_contents_func)(&arg, cpu);
> +        (*nf->note_contents_func)(&arg, cpu, id);
>   
>           note_size =
>               sizeof(arg.note) - sizeof(arg.note.contents) + nf->contents_size;

Reviewed-by: Thomas Huth <thuth@redhat.com>

Re: [PATCH 0/2] arch_dump: fix prstatus pid on s390x and ppc

[Thomas Huth]

On 19/06/2024 07.00, Omar Sandoval wrote:
> Hello,
> 
> I maintain drgn [1], a debugger for the Linux kernel. I ran into a quirk
> of the NT_PRSTATUS note in kernel core dumps [2], so I looked into how
> QEMU's dump-guest-memory command generates NT_PRSTATUS. I noticed that
> on most architectures, the note's PID field is set to the CPU ID plus 1.
> There are two exceptions: on s390x, there's an endianness bug (it's not
> byte swapped if the host is little endian), and on ppc, it's not set at
> all (it defaults to zero). They're both easy fixes.
> 
> Thanks,
> Omar
> 
> 1: https://github.com/osandov/drgn
> 2: https://github.com/osandov/drgn/issues/404
> 
> Omar Sandoval (2):
>    target/s390x/arch_dump: use correct byte order for pid
>    target/ppc/arch_dump: set prstatus pid to cpuid
> 
>   target/ppc/arch_dump.c   | 21 ++++++++++++---------
>   target/s390x/arch_dump.c |  2 +-
>   2 files changed, 13 insertions(+), 10 deletions(-)

I'm going to pick up patch 1 for my s390x tree ... for the second patch, it 
would be good if someone of the ppc guys could have a look at it first.

  Thomas

Re: [PATCH 2/2] target/ppc/arch_dump: set prstatus pid to cpuid

[Harsh Prateek Bora]

Hi Omar,

On 6/19/24 10:30, Omar Sandoval wrote:
> Every other architecture does this, and debuggers need it to be able to
> identify which prstatus note corresponds to which CPU.
> 
> Signed-off-by: Omar Sandoval <osandov@osandov.com>
> ---
>   target/ppc/arch_dump.c | 21 ++++++++++++---------
>   1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/target/ppc/arch_dump.c b/target/ppc/arch_dump.c
> index a8315659d9..78b4205319 100644
> --- a/target/ppc/arch_dump.c
> +++ b/target/ppc/arch_dump.c
> @@ -47,9 +47,11 @@ struct PPCUserRegStruct {
>   } QEMU_PACKED;
>   
>   struct PPCElfPrstatus {
> -    char pad1[112];
> +    char pad1[32];
> +    uint32_t pid;
> +    uint8_t pad2[76];
>       struct PPCUserRegStruct pr_reg;
> -    char pad2[40];
> +    char pad3[40];
>   } QEMU_PACKED;
>   

Could you please add a comment above the struct providing reference to 
the spec being referred here for member position across the status bits?

With that,

Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>

>   
> @@ -96,7 +98,7 @@ typedef struct NoteFuncArg {
>       DumpState *state;
>   } NoteFuncArg;
>   
> -static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       int i;
>       reg_t cr;
> @@ -109,6 +111,7 @@ static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
>   
>       prstatus = &note->contents.prstatus;
>       memset(prstatus, 0, sizeof(*prstatus));
> +    prstatus->pid = cpu_to_dump32(s, id);
>       reg = &prstatus->pr_reg;
>   
>       for (i = 0; i < 32; i++) {
> @@ -127,7 +130,7 @@ static void ppc_write_elf_prstatus(NoteFuncArg *arg, PowerPCCPU *cpu)
>       reg->ccr = cpu_to_dump_reg(s, cr);
>   }
>   
> -static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       int i;
>       struct PPCElfFpregset  *fpregset;
> @@ -146,7 +149,7 @@ static void ppc_write_elf_fpregset(NoteFuncArg *arg, PowerPCCPU *cpu)
>       fpregset->fpscr = cpu_to_dump_reg(s, cpu->env.fpscr);
>   }
>   
> -static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       int i;
>       struct PPCElfVmxregset *vmxregset;
> @@ -178,7 +181,7 @@ static void ppc_write_elf_vmxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
>       vmxregset->vscr.u32[3] = cpu_to_dump32(s, ppc_get_vscr(&cpu->env));
>   }
>   
> -static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       int i;
>       struct PPCElfVsxregset *vsxregset;
> @@ -195,7 +198,7 @@ static void ppc_write_elf_vsxregset(NoteFuncArg *arg, PowerPCCPU *cpu)
>       }
>   }
>   
> -static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu)
> +static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu, int id)
>   {
>       struct PPCElfSperegset *speregset;
>       Note *note = &arg->note;
> @@ -211,7 +214,7 @@ static void ppc_write_elf_speregset(NoteFuncArg *arg, PowerPCCPU *cpu)
>   
>   static const struct NoteFuncDescStruct {
>       int contents_size;
> -    void (*note_contents_func)(NoteFuncArg *arg, PowerPCCPU *cpu);
> +    void (*note_contents_func)(NoteFuncArg *arg, PowerPCCPU *cpu, int id);
>   } note_func[] = {
>       {sizeof_field(Note, contents.prstatus),  ppc_write_elf_prstatus},
>       {sizeof_field(Note, contents.fpregset),  ppc_write_elf_fpregset},
> @@ -282,7 +285,7 @@ static int ppc_write_all_elf_notes(const char *note_name,
>           arg.note.hdr.n_descsz = cpu_to_dump32(s, nf->contents_size);
>           strncpy(arg.note.name, note_name, sizeof(arg.note.name));
>   
> -        (*nf->note_contents_func)(&arg, cpu);
> +        (*nf->note_contents_func)(&arg, cpu, id);
>   
>           note_size =
>               sizeof(arg.note) - sizeof(arg.note.contents) + nf->contents_size;