In message <kexec-kern-2 at bga.com> you wrote: > The __kdump_flag ABI is overly constraining for future development. > > As of 2.6.27, the kernel entry point has 4 constraints: Offset 0 is > the starting point for the master (boot) cpu (entered with r3 pointing > to the device tree structure), offset 0x60 is code for the slave cpus > (entered with r3 set to their device tree physical id), offset 0x20 is > used by the iseries hypervisor, and secondary cpus must be well behaved > when the first 256 bytes are copied to address 0. > > Placing the __kdump_flag at 0x18 is bad because: > > - It was taking the last 8 bytes before the iseries hypervisor data. > - It was 8 bytes for a boolean flag > - It had no way of identifying that the flag was present > - It does leave any room for the master to add any additional code > before branching, which hurts debug. > - It will be unnecessarily hard for 32 bit code to be common (8 bytes) > > Now that we have eliminated the use of __kdump_flag in favor of > the standard is_kdump_kernel(), this flag only controls run without > relocating the kernel to PHYSICAL_START (0), so rename it __run_at_load. > > Move the flag to 0x5c, 1 word before the secondary cpu entry point at > 0x60. Use the copy at address 0 not the one in the base kernel image to > make it easier on kexec-tools. Initialize it with "run0" to say it will > run at 0 unless it is set to 1. It only exists if we are relocatable. > > Signed-off-by: Milton Miller <miltonm at bga.com> > --- > I left it global so it appears that way in System.map, but it would > not need to be. > > I kept the guards with CONFIG_CRASH_DUMP for now. They could be relaxed > to just CONFIG_RELOCATABLE. > > Tested with normal kexec (kernel moved to 0) and a custom boot-loader > (kernel stayed at loaded 16MB start). > > Index: next.git/arch/powerpc/kernel/head_64.S > =================================================================== > --- next.git.orig/arch/powerpc/kernel/head_64.S 2008-10-22 04:30:08.000 000000 -0500 > +++ next.git/arch/powerpc/kernel/head_64.S 2008-10-22 04:59:55.000000000 - 0500 > @@ -97,12 +97,6 @@ __secondary_hold_spinloop: > __secondary_hold_acknowledge: > .llong 0x0 > > - /* This flag is set by purgatory if we should be a kdump kernel. */ > - /* Do not move this variable as purgatory knows about it. */ > - .globl __kdump_flag > -__kdump_flag: > - .llong 0x0 > - > #ifdef CONFIG_PPC_ISERIES > /* > * At offset 0x20, there is a pointer to iSeries LPAR data. > @@ -112,6 +106,20 @@ __kdump_flag: > .llong hvReleaseData-KERNELBASE > #endif /* CONFIG_PPC_ISERIES */ > > +#ifdef CONFIG_CRASH_DUMP > + /* This flag is set to 1 by a loader if the kernel should run > + * at the loaded address instead of the linked address. This > + * is used by kexec-tools to keep the the kdump kernel in the > + * crash_kernel region. The loader is responsible for > + * observing the alignment requirement. > + */ > + /* Do not move this variable as kexec-tools knows about it. */ > + . = 0x5c > + .globl __run_at_load > +__run_at_load: > + .long 0x72756e30 /* "run0" -- relocate to 0 by default */ > +#endif > + > . = 0x60 > /* > * The following code is used to hold secondary processors > @@ -1391,8 +1399,8 @@ _STATIC(__after_prom_start) > lis r25,PAGE_OFFSET at highest /* compute virtual base of kernel */ > sldi r25,r25,32 > #ifdef CONFIG_CRASH_DUMP > - ld r7,__kdump_flag-_stext(r26) > - cmpldi cr0,r7,1 /* kdump kernel ? - stay where we are */ > + lwz r7,__run_at_load-_stext(0) > + cmplwi cr0,r7,1 /* kdump kernel ? - stay where we are */ Do we really want the flag to always be at 0x5c not 0x5c + kernel offset? Also, comment "kdump kernel" needs to be updated to reflect the new name. Other than that, the patch series works for me. Mikey > bne 1f > add r25,r25,r26 > #endif > @@ -1416,11 +1424,11 @@ _STATIC(__after_prom_start) > #ifdef CONFIG_CRASH_DUMP > /* > * Check if the kernel has to be running as relocatable kernel based on the > - * variable __kdump_flag, if it is set the kernel is treated as relocatable > + * variable __run_at_load, if it is set the kernel is treated as relocatable > * kernel, otherwise it will be moved to PHYSICAL_START > */ > - ld r7,__kdump_flag-_stext(r26) > - cmpldi cr0,r7,1 > + lwz r7,__run_at_load-_stext(0) > + cmplwi cr0,r7,1 > bne 3f > > li r5,__end_interrupts - _stext /* just copy interrupts */ > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev at ozlabs.org > https://ozlabs.org/mailman/listinfo/linuxppc-dev >
