[Crash-utility] [PATCH 01/16] Add MIPS64 framework code support

[HAGIO KAZUHITO(萩尾 一仁)]

-----Original Message-----
> Hi Kazu,
> 
> On 03/12/2021 12:21 PM, HAGIO KAZUHITO(萩尾　一仁) wrote:
> 
> > -----Original Message-----
> >>>> --- a/diskdump.c
> >>>> +++ b/diskdump.c
> >>>> @@ -594,6 +594,9 @@ restart:
> >>>>    	else if (STRNEQ(header->utsname.machine, "mips") &&
> >>>>    	    machine_type_mismatch(file, "MIPS", NULL, 0))
> >>>>    		goto err;
> >>>> +	else if (STRNEQ(header->utsname.machine, "mips64") &&
> >>>> +	    machine_type_mismatch(file, "MIPS", NULL, 0))
> >>>> +		goto err;
> >>> Why do you make MACHINE_TYPE the same as the MIPS one?
> >>> With this, doesn't a MIPS64 crash match a MIPS vmcore?
> >> The value of the machine type e_machine in mips32 or mips64 is MIPS, which
> >> corresponds to EM_MIPS.
> >> The definition in gdb-7.6/include/elf/common.h:110 is as follows:
> >>       #define EM_MIPS        8        /* MIPS R3000 */
> >> But there is no related definition of EM_MIPS64 or other mips64, so both
> >> mips32 and mips64 should use EM_MIPS, and the corresponding e_machine is
> >> MIPS.
> >>
> >> If the MACHINE_TYPE of mips64 is defined as MIPS64, as follows:
> >>       define MACHINE_TYPE     "MIPS64"
> >>
> >> The following error will appear when running crash:
> >>       WARNING: machine type mismatch:
> >>                 crash utility: MIPS64
> >>                 vmcore: MIPS
> > Then, is there any problem with this?
> >    machine_type_mismatch(file, "MIPS64", NULL, 0))
> >
> > This can prevent a mips64 crash from trying to open a mips32 vmcore
> > and the reverse.
> Read the ELF header information of vmocre (whether it is mips32 or mips64),
> and the obtained machine type is MIPS, not MIPS64. In mips64, if you use
> machine_type_mismatch(file, "MIPS64", NULL, 0)), there will be a machine
> type
> mismatch. You can only use machine_type_mismatch(file, "MIPS", NULL, 0)),
> only then It can be successfully matched to the machine type.

Probably I misunderstand something, but then need to know it..

The machine_type_mismatch() doesn't use the ELF's EM_MIPS value.
Why do we need to match crash's MACHINE_TYPE with ELF's EM_MIPS?

int
machine_type(char *type)
{
        return STREQ(MACHINE_TYPE, type);
}

int 
machine_type_mismatch(char *file, char *e_machine, char *alt, ulong query)
{
        if (machine_type(e_machine) || machine_type(alt))
                return FALSE;

        if (query == KDUMP_LOCAL)  /* already printed by NETDUMP_LOCAL */
                return TRUE;

        error(WARNING, "machine type mismatch:\n");

        fprintf(fp, "         crash utility: %s\n", MACHINE_TYPE);
        fprintf(fp, "         %s: %s%s%s\n\n", file, e_machine,
                alt ? " or " : "", alt ? alt : "");
                
        return TRUE;
}

Without the following hunk, EM_MIPS has been used only for ELF32 in symbols.c.

--- a/symbols.c
+++ b/symbols.c
@@ -3636,6 +3636,11 @@ is_kernel(char *file)
                                goto bailout;
                        break;
 
+               case EM_MIPS:
+                       if (machine_type_mismatch(file, "MIPS", NULL, 0))
+                               goto bailout;
+                       break;
+
                default:
                        if (machine_type_mismatch(file, "(unknown)", NULL, 0)) 
                                goto bailout;
@@ -3890,6 +3895,11 @@ is_shared_object(char *file)
                        if (machine_type("SPARC64"))
                                return TRUE;
                        break;
+
+               case EM_MIPS:
+                       if (machine_type("MIPS"))
+                               return TRUE;
+                       break;
                }   

So I thought that meybe we can also change these ELF64 cases to "MIPS64"
with defining MACHINE_TYPE as "MIPS64".

This is wrong?  e.g. mips32 also can use an ELF64 kernel/module binary?

Thanks,
Kazu

> >
> >> # readelf -h vmcore
> >> ...
> >>     Type:                              CORE (Core file)
> >>     Machine:                           MIPS R3000
> >> ...
> >>
> >> Therefore, the MACHINE_TYPE of mips32 and mips64 both define MIPS.
> >>
> >> Thanks,
> >> Youling