Marshall Dawson has uploaded this change for review.
[NOT FOR MERGE]: Demo adding near_reset_vector symbol
In https://review.coreboot.org/c/coreboot/+/35035/8/src/arch/x86/early_dram.ld
we had a discussion about whether an approach like for RESET_VECTOR_IN_RAM
could potentially be used for a bootblock that needed to grow >64KB (to keep
the first 16-bit jmp within reach).
This is a mockup of the test I ran to verify that would be practical. Using
this code I built a google/grunt and recorded the following with readelf.
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .text PROGBITS ffff0000 000060 0059d0 00 AX 0 0 32
[ 2] .rel.text REL 00000000 01335c 001378 08 I 10 1 4
[ 3] .car.data NOBITS 00030000 000000 005860 00 WA 0 0 4
[ 4] .near_reset_vecto PROGBITS fffffe00 00fe60 0000bb 00 AX 0 0 4
[ 5] .rel.near_reset_v REL 00000000 0146d4 000040 08 I 10 4 4
[ 6] .reset PROGBITS fffffff0 010050 000010 00 AX 0 0 1
[ 7] .rel.reset REL 00000000 014714 000008 08 I 10 6 4
[ 8] .id PROGBITS ffffff4a 00ffaa 000036 00 A 0 0 1
[ 9] .gnu_debuglink PROGBITS 00000000 010060 000014 00 0 0 4
[10] .symtab SYMTAB 00000000 010074 001a80 10 11 243 4
[11] .strtab STRTAB 00000000 011af4 001868 00 0 0 1
[12] .shstrtab STRTAB 00000000 01471c 000064 00 0 0 1
Note, however, that I did not grow the bootblock.elf file; only inserted the
section and relocated the _start16bit code.
fffffe00 <_start16bit>:
fffffe00: fa cli
fffffe01: 66 89 c5 mov %ax,%bp
fffffe04: b0 01 mov $0x1,%al
fffffe06: e6 80 out %al,$0x80
fffffe08: 66 31 c0 xor %ax,%ax
fffffe0b: 0f 22 d8 mov %eax,%cr3
fffffe0e: 8c c8 mov %cs,%eax
fffffe10: c1 e0 04 shl $0x4,%eax
fffffe13: bb 4c fe 29 c3 mov $0xc329fe4c,%ebx
fffffe18: 2e 0f 01 1f lidtl %cs:(%edi)
fffffe1c: bb 44 fe 29 c3 mov $0xc329fe44,%ebx
fffffe21: 2e 66 0f 01 17 lgdtw %cs:(%edi)
fffffe26: 0f 20 c0 mov %cr0,%eax
fffffe29: 66 25 d1 ff and $0xffd1,%ax
fffffe2d: fa cli
fffffe2e: 7f 66 jg fffffe96 <__protected_start+0xb>
fffffe30: 0d 01 00 00 60 or $0x60000001,%eax
fffffe35: 0f 22 c0 mov %eax,%cr0
fffffe38: 66 89 e8 mov %bp,%ax
fffffe3b: 66 ea 8b fe ff ff ljmpw $0xffff,$0xfe8b
fffffe41: 08 00 or %al,(%eax)
fffffe43: 90 nop
Growing the elf should be reasonably straightforward. Right now reset16.ld
has a built-in assumption of 64KB. For RESET_VECTOR_IN_RAM I've added a
size symbol to Kconfig (yet to land still) for locating the reset vector
and near_reset_vector at the very top, and so that the calculations are
expected to match the instructions given to the PSP.
Change-Id: I6e7888c778e1d1cc426e4160543f4a4662ebf834
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
---
M src/cpu/x86/16bit/entry16.inc
M src/cpu/x86/16bit/reset16.ld
2 files changed, 11 insertions(+), 0 deletions(-)
git pull ssh://review.coreboot.org:29418/coreboot refs/changes/18/36418/1
diff --git a/src/cpu/x86/16bit/entry16.inc b/src/cpu/x86/16bit/entry16.inc
index 9e00c55..6062abd 100644
--- a/src/cpu/x86/16bit/entry16.inc
+++ b/src/cpu/x86/16bit/entry16.inc
@@ -37,6 +37,9 @@
.align 4096
#endif
.code16
+
+.section ".near_reset_vector", "ax", %progbits
+
.globl _start16bit
.type _start16bit, @function
diff --git a/src/cpu/x86/16bit/reset16.ld b/src/cpu/x86/16bit/reset16.ld
index c57cc96..31716e0 100644
--- a/src/cpu/x86/16bit/reset16.ld
+++ b/src/cpu/x86/16bit/reset16.ld
@@ -17,6 +17,14 @@
*/
SECTIONS {
+ _ROMTOP = 0xfffffff0;
+ _NEAR_RESET_VECTOR = _ROMTOP + 0x10 - 0x200;
+
+ . = _NEAR_RESET_VECTOR;
+ .near_reset_vector . : {
+ *(.near_reset_vector);
+ }
+
/* Trigger an error if I have an unuseable start address */
_bogus = ASSERT(_start16bit >= 0xffff0000, "_start16bit too low. Please report.");
_ROMTOP = 0xfffffff0;
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