On Mon, 2 Mar 2020 at 00:05, Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote: > > In preparation for being able to decompress starting at a different > address than startup_32, save the calculated output address instead of > recalculating it later. > Could you expand this a bit? Are you talking about *running* the decompressor code at another offset? Or about the space it uses. I think I know but I'd like to be sure :-) > We now keep track of three addresses: > %edx: startup_32 as we were loaded by bootloader > %ebx: new location of compressed kernel > %ebp: start of decompression buffer > > Signed-off-by: Arvind Sankar <nivedita@xxxxxxxxxxxx> > --- > arch/x86/boot/compressed/head_32.S | 25 ++++++++++++------------- > 1 file changed, 12 insertions(+), 13 deletions(-) > > diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S > index 46bbe7ab4adf..894182500606 100644 > --- a/arch/x86/boot/compressed/head_32.S > +++ b/arch/x86/boot/compressed/head_32.S > @@ -75,11 +75,11 @@ SYM_FUNC_START(startup_32) > */ > leal (BP_scratch+4)(%esi), %esp > call 1f > -1: popl %ebp > - subl $1b, %ebp > +1: popl %edx > + subl $1b, %edx > > /* Load new GDT */ > - leal gdt(%ebp), %eax > + leal gdt(%edx), %eax > movl %eax, 2(%eax) > lgdt (%eax) > > @@ -92,13 +92,14 @@ SYM_FUNC_START(startup_32) > movl %eax, %ss > > /* > - * %ebp contains the address we are loaded at by the boot loader and %ebx > + * %edx contains the address we are loaded at by the boot loader and %ebx > * contains the address where we should move the kernel image temporarily > - * for safe in-place decompression. > + * for safe in-place decompression. %ebp contains the address that the kernel > + * will be decompressed to. > */ > > #ifdef CONFIG_RELOCATABLE > - movl %ebp, %ebx > + movl %edx, %ebx > movl BP_kernel_alignment(%esi), %eax > decl %eax > addl %eax, %ebx > @@ -110,10 +111,10 @@ SYM_FUNC_START(startup_32) > movl $LOAD_PHYSICAL_ADDR, %ebx > 1: > > + movl %ebx, %ebp // Save the output address for later > /* Target address to relocate to for decompression */ > - movl BP_init_size(%esi), %eax > - subl $_end, %eax > - addl %eax, %ebx > + addl BP_init_size(%esi), %ebx > + subl $_end, %ebx > > /* Set up the stack */ > leal boot_stack_end(%ebx), %esp > @@ -127,7 +128,7 @@ SYM_FUNC_START(startup_32) > * where decompression in place becomes safe. > */ > pushl %esi > - leal (_bss-4)(%ebp), %esi > + leal (_bss-4)(%edx), %esi > leal (_bss-4)(%ebx), %edi > movl $(_bss - startup_32), %ecx > shrl $2, %ecx > @@ -196,9 +197,7 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) > /* push arguments for extract_kernel: */ > pushl $z_output_len /* decompressed length, end of relocs */ > > - leal _end(%ebx), %eax > - subl BP_init_size(%esi), %eax > - pushl %eax /* output address */ > + pushl %ebp /* output address */ > > pushl $z_input_len /* input_len */ > leal input_data(%ebx), %eax > -- > 2.24.1 >
