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Spend some bytes of code in stub to eliminate wasted stack space.

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(Choose between this revision and previous, according to taste.)
	fold_elf86.asm l_lx_elf.c

committer: jreiser <jreiser> 994887023 +0000
This commit is contained in:
John Reiser 2001-07-11 21:30:23 +00:00
parent ef17dc10ca
commit 96141d82f4
2 changed files with 82 additions and 43 deletions
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99
src/stub/fold_elf86.asm
View File

@ -49,56 +49,42 @@ fold_begin: ; enter: %ebx= &Elf32_Ehdr of this program
pop eax ; discard &sz_uncompressed
pop eax ; discard sz_uncompressed
; Move argc,argv,envp down to make room for complete Elf_auxv table.
; ld-linux.so.2 depends on AT_PHDR and AT_ENTRY, for instance.
; Move argc,argv,envp down to make room for Elf_auxv table.
; Linux kernel 2.4.2 and earlier give only AT_HWCAP and AT_PLATFORM
; because we have no PT_INTERP. Linux kernel 2.4.5 (and later?)
; give not quite everything. It is simpler and smaller code for us
; to generate a "complete" table where Elf_auxv[k -1].a_type = k.
; ld-linux.so.2 depends on AT_PHDR and AT_ENTRY, for instance
; On second thought, that wastes a lot of stack space (the entire kernel
; auxv, plus those slots that remain empty anyway). So try for minimal
; space on stack, without too much code, by doing it serially.
%define AT_NULL 0
%define AT_IGNORE 1
%define AT_PHDR 3
%define AT_PHENT 4
%define AT_PHNUM 5
%define AT_PAGESZ 6
%define AT_ENTRY 9
%define AT_NUMBER 20
sub ecx, ecx
mov edx, (1<<AT_PHDR) | (1<<AT_PHENT) | (1<<AT_PHNUM) | (1<<AT_PAGESZ) | (1<<AT_ENTRY)
mov esi, esp
sub esp, sz_auxv * AT_NUMBER ; more than 128 bytes
mov edi, esp
do_auxv: ; entry: %esi=src = &argc; %edi=dst. exit: %edi= &AT_NULL
; cld
call do_auxv ; clear bits in edx according to existing auxv slots
L10: ; move argc+argv
lodsd
stosd
test eax,eax
jne L10
mov esi, esp
L50:
shr edx, 1 ; Carry = bottom bit
sbb eax, eax ; -1 or 0
sub ecx, eax ; count of 1 bits that remained in edx
lea esp, [esp + sz_auxv * eax] ; allocate one auxv slot, if needed
test edx,edx
jne L50
L20: ; move envp
lodsd
stosd
test eax,eax
jne L20
; complete Elf_auxv table full of AT_IGNORE
push edi ; save base of resulting table
inc eax ; convert 0 to AT_IGNORE
mov ecx, 2 * (AT_NUMBER -1)
rep stosd
dec eax ; convert AT_IGNORE into AT_NULL
stosd ; terminate Elf_auxv
stosd
pop edi ; base of resulting table
L30: ; distribute existing Elf32_auxv into new table
lodsd
test eax,eax ; AT_NULL ?
xchg eax,edx
lodsd
je L40
mov [a_type + sz_auxv*(edx -1) + edi], edx
mov [a_val + sz_auxv*(edx -1) + edi], eax
jmp L30
L40:
mov edi, esp
call do_auxv ; move; fill new auxv slots with AT_IGNORE
%define OVERHEAD 2048
%define MAX_ELF_HDR 512
@ -149,5 +135,46 @@ EXTERN make_hatch
mov eax, __NR_munmap ; do not dirty the stack with push byte + pop
jmp edx ; unmap ourselves via escape hatch, then goto entry
; called twice:
; 1st with esi==edi, ecx=0, edx= bitmap of slots needed: just update edx.
; 2nd with esi!=edi, ecx= slot_count: move, then append AT_IGNORE slots
; entry: esi= src = &argc; edi= dst; ecx= # slots wanted; edx= bits wanted
; exit: edi= &auxtab; edx= bits still needed
do_auxv:
; cld
L10: ; move argc+argv
lodsd
stosd
test eax,eax
jne L10
L20: ; move envp
lodsd
stosd
test eax,eax
jne L20
push edi ; return value
L30: ; process auxv
lodsd ; a_type
stosd
btr edx, eax ; no longer need a slot of type eax
test eax, eax ; AT_NULL ?
lodsd
stosd
jne L30
sub edi, byte 8 ; backup to AT_NULL
add ecx, ecx ; two words per auxv
inc eax ; convert 0 to AT_IGNORE
rep stosd ; allocate and fill
dec eax ; convert AT_IGNORE to AT_NULL
stosd ; re-terminate with AT_NULL
stosd
pop edi ; &auxtab
ret
; vi:ts=8:et:nowrap

26
src/stub/l_lx_elf.c
View File

@ -212,6 +212,18 @@ bzero(char *p, size_t len)
}
static void
auxv_up(Elf32_auxv_t *av, int const type, unsigned const value)
{
for (;; ++av) {
if (av->a_type==type || av->a_type==AT_IGNORE) {
av->a_type = type;
av->a_un.a_val = value;
return;
}
}
}
static Elf32_Addr // entry address
do_xmap(int const fdi, Elf32_Ehdr const *const ehdr, struct Extent *const xi,
Elf32_auxv_t *const av)
@ -222,7 +234,7 @@ do_xmap(int const fdi, Elf32_Ehdr const *const ehdr, struct Extent *const xi,
int j;
for (j=0; j < ehdr->e_phnum; ++phdr, ++j)
if (PT_PHDR==phdr->p_type) {
av[AT_PHDR -1].a_un.a_val = phdr->p_vaddr;
auxv_up(av, AT_PHDR, phdr->p_vaddr);
}
else if (PT_LOAD==phdr->p_type) {
struct Extent xo;
@ -346,12 +358,12 @@ void *upx_main(
xi.buf -= sz_pckhdrs;
xi.size = sz_compressed;
// av[AT_PHDR -1].a_un.a_val is set again by do_xmap if PT_PHDR is present.
av[AT_PHDR -1].a_type = AT_PHDR ; av[AT_PHDR -1].a_un.a_ptr = 1+(Elf32_Ehdr *)phdr->p_vaddr;
av[AT_PHENT -1].a_type = AT_PHENT ; av[AT_PHENT -1].a_un.a_val = ehdr->e_phentsize;
av[AT_PHNUM -1].a_type = AT_PHNUM ; av[AT_PHNUM -1].a_un.a_val = ehdr->e_phnum;
av[AT_PAGESZ -1].a_type = AT_PAGESZ; av[AT_PAGESZ -1].a_un.a_val = PAGE_SIZE;
av[AT_ENTRY -1].a_type = AT_ENTRY ; av[AT_ENTRY -1].a_un.a_val = ehdr->e_entry;
// AT_PHDR.a_un.a_val is set again by do_xmap if PT_PHDR is present.
auxv_up(av, AT_PHDR , (unsigned)(1+(Elf32_Ehdr *)phdr->p_vaddr));
auxv_up(av, AT_PHENT , ehdr->e_phentsize);
auxv_up(av, AT_PHNUM , ehdr->e_phnum);
//auxv_up(av, AT_PAGESZ, PAGE_SIZE); /* ld-linux.so.2 does not need this */
auxv_up(av, AT_ENTRY , (unsigned)ehdr->e_entry);
entry = do_xmap((int)f_decompress, ehdr, &xi, av);
{ // Map PT_INTERP program interpreter