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author | H. Peter Anvin <hpa@zytor.com> | 2008-02-01 15:45:51 -0800 |
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committer | H. Peter Anvin <hpa@zytor.com> | 2008-02-01 15:45:51 -0800 |
commit | 09ccf87391c3fafd89093b77284b6beaca3c97e0 (patch) | |
tree | 0c1ac29a1aac3162ef4be323a7bebdb0bb2e50f5 | |
parent | 50644f57d7b7481e27a9f75ab038ae9effd82e96 (diff) | |
download | syslinux-09ccf87391c3fafd89093b77284b6beaca3c97e0.tar.gz |
E820 parser: handle BIOSes with multiple contiguous regions
Well, it has finally happened: a bug report regarding a BIOS with
emits multiple contiguous memory regions. Handle that case, and
(hopefully) simplify the logic while we're at it.
-rw-r--r-- | highmem.inc | 78 |
1 files changed, 41 insertions, 37 deletions
diff --git a/highmem.inc b/highmem.inc index a2cc7ac5..1cd46dd9 100644 --- a/highmem.inc +++ b/highmem.inc @@ -21,20 +21,26 @@ ; ; This is set up as a subroutine; it will set up the global variable -; HighMemSize. All registers are preserved. Assumes DS == CS. +; HighMemSize. All registers are preserved. ; highmemsize: push es pushad + push cs + pop es + ; ; First, try INT 15:E820 (get BIOS memory map) ; +; Note: we may have to scan this multiple times, because some (daft) BIOSes +; report main memory as multiple contiguous ranges... +; get_e820: - xor ebx,ebx ; Start with first record mov dword [E820Max],-(1 << 20) ; Max amount of high memory - mov dword [E820Mem],ebx ; Detected amount of high memory - mov es,bx ; Need ES = DS = 0 for now + mov dword [E820Mem],(1 << 20) ; End of detected high memory +.start_over: + xor ebx,ebx ; Start with first record jmp short .do_e820 ; Skip "at end" check first time! .int_loop: and ebx,ebx ; If we're back at beginning... jz .e820_done ; ... we're done @@ -57,45 +63,44 @@ get_e820: ; cmp dword [E820Buf+4], byte 0 ja .int_loop ; Start >= 4 GB? - mov edx, (1 << 20) - sub edx, [E820Buf] - jnb .ram_range ; Start >= 1 MB? - ; If we get here, it starts > 1 MB but < 4 GB; if this is a - ; *non*-memory range, remember this as unusable; some BIOSes - ; get the length of primary RAM wrong! - cmp dword [E820Buf+16], byte 1 - je .int_loop ; If it's memory, don't worry about it - neg edx ; This means what for memory limit? - cmp edx,[E820Max] ; Better or worse - jnb .int_loop - mov [E820Max],edx + mov eax, [E820Buf] + cmp dword [E820Buf+16],1 + je .is_ram ; Is it memory? + ; + ; Non-memory range. Remember this as a limit; some BIOSes get the length + ; of primary RAM incorrect! + ; + cmp eax, (1 << 20) + jb .int_loop ; Starts in lowmem region + cmp eax,[E820Max] + jae .int_loop ; Already above limit + mov [E820Max],eax ; Set limit jmp .int_loop -.ram_range: - stc - sbb eax,eax ; eax <- 0xFFFFFFFF - cmp dword [E820Buf+12], byte 0 - ja .huge ; Size >= 4 GB - mov eax, [E820Buf+8] -.huge: sub eax, edx ; Adjust size to start at 1 MB - jbe .int_loop ; Completely below 1 MB? - - ; Now EAX contains the size of memory 1 MB...up - cmp dword [E820Buf+16], byte 1 - jne .int_loop ; High memory isn't usable memory!!!! - - ; We're good! +.is_ram: + cmp eax,[E820Mem] + ja .int_loop ; Not contiguous with our starting point + add eax,[E820Buf+8] + jc .overflow + cmp dword [E820Buf+12],0 + je .nooverflow +.overflow: + or eax,-1 +.nooverflow: + cmp eax,[E820Mem] + jbe .int_loop ; All is below our baseline mov [E820Mem],eax - jmp .int_loop ; Still need to add low 1 MB + jmp .start_over ; Start over in case we find an adjacent range .e820_done: mov eax,[E820Mem] - and eax,eax - jz no_e820 ; Nothing found by E820? - cmp eax,[E820Max] ; Make sure we're not limited - jna got_highmem_add1mb + cmp eax,[E820Max] + jna .not_limited mov eax,[E820Max] - jmp got_highmem_add1mb +.not_limited: + cmp eax,(1 << 20) + ja got_highmem ; Did we actually find memory? + ; otherwise fall through ; ; INT 15:E820 failed. Try INT 15:E801. @@ -125,7 +130,6 @@ no_e801: e801_hole: and eax,0ffffh shl eax,10 ; Convert from kilobytes -got_highmem_add1mb: add eax,(1 << 20) ; First megabyte got_highmem: %if HIGHMEM_SLOP != 0 |