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[ELF][MIPS] Fix calculation of GOT "page address" entries number 

If output section which referenced by R_MIPS_GOT_PAGE or R_MIPS_GOT16
relocations is small (less that 0x10000 bytes) and occupies two adjacent
0xffff-bytes pages, current formula gives incorrect number of required "page"
GOT entries. The problem is that in time of calculation we do not know
the section address and so we cannot calculate number of 0xffff-bytes
pages exactly.

This patch fix the formula. Now it gives a correct number of pages in
the worst case when "small" section intersects 0xffff-bytes page
boundary. From the other side, sometimes it adds one more redundant GOT
entry for each output section. But usually number of output sections
referenced by GOT relocations is small.

llvm-svn: 288127
This commit is contained in:
Simon Atanasyan 2016-11-29 10:23:46 +00:00
parent c211c6c884
commit 80f3d9ce93
6 changed files with 86 additions and 22 deletions
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6
lld/ELF/SyntheticSections.cpp
View File

@ -538,7 +538,7 @@ MipsGotSection<ELFT>::getPageEntryOffset(uintX_t EntryValue) {
// See comment in the MipsGotSection::writeTo.
size_t NewIndex = PageIndexMap.size() + 2;
auto P = PageIndexMap.insert(std::make_pair(EntryValue, NewIndex));
assert(!P.second || PageIndexMap.size() <= PageEntriesNum);
assert(!P.second || PageIndexMap.size() <= (PageEntriesNum - 2));
return (uintX_t)P.first->second * sizeof(uintX_t);
}
@ -594,14 +594,14 @@ template <class ELFT> void MipsGotSection<ELFT>::finalize() {
size_t EntriesNum = TlsEntries.size();
// Take into account MIPS GOT header.
// See comment in the MipsGotSection::writeTo.
PageEntriesNum += 2;
PageEntriesNum = 2;
for (const OutputSectionBase *OutSec : OutSections) {
// Calculate an upper bound of MIPS GOT entries required to store page
// addresses of local symbols. We assume the worst case - each 64kb
// page of the output section has at least one GOT relocation against it.
// Add 0x8000 to the section's size because the page address stored
// in the GOT entry is calculated as (value + 0x8000) & ~0xffff.
PageEntriesNum += (OutSec->Size + 0x8000 + 0xfffe) / 0xffff;
PageEntriesNum += (OutSec->Size + 0xfffe) / 0xffff + 1;
}
EntriesNum += getLocalEntriesNum() + GlobalEntries.size();
Size = EntriesNum * sizeof(uintX_t);

17
lld/test/ELF/mips-64-got.s
View File

@ -14,9 +14,9 @@
# CHECK-NEXT: 20000: df 82 80 20 ld $2, -32736($gp)
# CHECK-NEXT: 20004: 64 42 00 18 daddiu $2, $2, 24
# CHECK-NEXT: 20008: 24 42 80 38 addiu $2, $2, -32712
# CHECK-NEXT: 2000c: 24 42 80 28 addiu $2, $2, -32728
# CHECK-NEXT: 20010: 24 42 80 30 addiu $2, $2, -32720
# CHECK-NEXT: 20008: 24 42 80 40 addiu $2, $2, -32704
# CHECK-NEXT: 2000c: 24 42 80 30 addiu $2, $2, -32720
# CHECK-NEXT: 20010: 24 42 80 38 addiu $2, $2, -32712
# CHECK: 0000000000020018 .text 00000000 foo
# CHECK: 0000000000037ff0 .got 00000000 .hidden _gp
@ -50,18 +50,23 @@
# GOT-NEXT: Entry {
# GOT-NEXT: Address: 0x30018
# GOT-NEXT: Access: -32728
# GOT-NEXT: Initial: 0x20014
# GOT-NEXT: Initial: 0x0
# GOT-NEXT: }
# GOT-NEXT: Entry {
# GOT-NEXT: Address: 0x30020
# GOT-NEXT: Access: -32720
# GOT-NEXT: Initial: 0x20014
# GOT-NEXT: }
# GOT-NEXT: Entry {
# GOT-NEXT: Address: 0x30028
# GOT-NEXT: Access: -32712
# GOT-NEXT: Initial: 0x20018
# GOT-NEXT: }
# GOT-NEXT: ]
# GOT-NEXT: Global entries [
# GOT-NEXT: Entry {
# GOT-NEXT: Address: 0x30028
# GOT-NEXT: Access: -32712
# GOT-NEXT: Address: 0x30030
# GOT-NEXT: Access: -32704
# GOT-NEXT: Initial: 0x0
# GOT-NEXT: Value: 0x0
# GOT-NEXT: Type: Function

40
lld/test/ELF/mips-got-page.s Normal file
View File

@ -0,0 +1,40 @@
# Check the case when small section (less that 0x10000 bytes) occupies
# two adjacent 0xffff-bytes pages. We need to create two GOT entries
# for R_MIPS_GOT_PAGE relocations.
# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-linux -o %t.o %s
# RUN: ld.lld --section-start .rodata=0x27FFC -shared -o %t.so %t.o
# RUN: llvm-readobj -t -mips-plt-got %t.so | FileCheck %s
# REQUIRES: mips
# CHECK: Name: bar
# CHECK-NEXT: Value: 0x28000
# ^ page-address = (0x28000 + 0x8000) & ~0xffff = 0x30000
# CHECK: Name: foo
# CHECK-NEXT: Value: 0x27FFC
# ^ page-address = (0x27ffc + 0x8000) & ~0xffff = 0x20000
# CHECK: Local entries [
# CHECK-NEXT: Entry {
# CHECK-NEXT: Address:
# CHECK-NEXT: Access: -32736
# CHECK-NEXT: Initial: 0x20000
# CHECK-NEXT: }
# CHECK-NEXT: Entry {
# CHECK-NEXT: Address:
# CHECK-NEXT: Access: -32728
# CHECK-NEXT: Initial: 0x30000
# CHECK-NEXT: }
# CHECK-NEXT: ]
.text
ld $v0,%got_page(foo)($gp)
ld $v0,%got_page(bar)($gp)
.rodata
foo:
.word 0
bar:
.word 0

6
lld/test/ELF/mips-got-redundant.s
View File

@ -22,6 +22,12 @@
# CHECK-NEXT: Entry {
# CHECK-NEXT: Address: 0x20010
# CHECK-NEXT: Access: -32736
# CHECK-NEXT: Initial: 0x0
# ^-- redundant
# CHECK-NEXT: }
# CHECK-NEXT: Entry {
# CHECK-NEXT: Address: 0x20014
# CHECK-NEXT: Access: -32732
# CHECK-NEXT: Initial: 0x40008
# ^-- glb1
# CHECK-NEXT: }

22
lld/test/ELF/mips-got16.s
View File

@ -17,9 +17,9 @@
# CHECK-NEXT: 10014: 21 08 90 04 addi $8, $8, -28668
# CHECK-NEXT: 10018: 8f 88 80 20 lw $8, -32736($gp)
# CHECK-NEXT: 1001c: 21 08 10 04 addi $8, $8, 4100
# CHECK-NEXT: 10020: 8f 88 80 28 lw $8, -32728($gp)
# CHECK-NEXT: 10020: 8f 88 80 30 lw $8, -32720($gp)
# CHECK-NEXT: 10024: 21 08 10 08 addi $8, $8, 4104
# CHECK-NEXT: 10028: 8f 88 80 2c lw $8, -32724($gp)
# CHECK-NEXT: 10028: 8f 88 80 34 lw $8, -32716($gp)
#
# CHECK: SYMBOL TABLE:
# CHECK: 00051008 .data 00000000 .hidden bar
@ -72,15 +72,27 @@
# GOT-NEXT: }
# GOT-NEXT: Entry {
# GOT-NEXT: Address: 0x20018
# GOT-NEXT: Access: -327
# GOT-NEXT: Access: -32728
# GOT-NEXT: Initial: 0x0
# ^-- redundant unused entry
# GOT-NEXT: }
# GOT-NEXT: Entry {
# GOT-NEXT: Address: 0x2001C
# GOT-NEXT: Access: -32724
# GOT-NEXT: Initial: 0x0
# ^-- redundant unused entry
# GOT-NEXT: }
# GOT-NEXT: Entry {
# GOT-NEXT: Address: 0x20020
# GOT-NEXT: Access: -32720
# GOT-NEXT: Initial: 0x51008
# ^-- 'bar' address
# GOT-NEXT: }
# GOT-NEXT: ]
# GOT-NEXT: Global entries [
# GOT-NEXT: Entry {
# GOT-NEXT: Address: 0x2001C
# GOT-NEXT: Access: -32724
# GOT-NEXT: Address: 0x20024
# GOT-NEXT: Access: -32716
# GOT-NEXT: Initial: 0x0
# GOT-NEXT: Value: 0x0
# GOT-NEXT: Type: None

17
lld/test/ELF/mips-xgot-order.s
View File

@ -10,22 +10,23 @@
# CHECK: Disassembly of section .text:
# CHECK-NEXT: __start:
# CHECK-NEXT: 20000: 3c 02 00 00 lui $2, 0
# CHECK-NEXT: 20004: 8c 42 80 20 lw $2, -32736($2)
# CHECK-NEXT: 20004: 8c 42 80 24 lw $2, -32732($2)
# CHECK-NEXT: 20008: 3c 02 00 00 lui $2, 0
# CHECK-NEXT: 2000c: 8c 42 80 24 lw $2, -32732($2)
# CHECK-NEXT: 2000c: 8c 42 80 28 lw $2, -32728($2)
#
# CHECK: bar:
# CHECK-NEXT: 20010: 8c 42 80 1c lw $2, -32740($2)
# CHECK-NEXT: 20010: 8c 42 80 20 lw $2, -32736($2)
# CHECK-NEXT: 20014: 8c 42 80 18 lw $2, -32744($2)
# CHECK-NEXT: 20018: 20 42 00 00 addi $2, $2, 0
# CHECK: Contents of section .got:
# CHECK-NEXT: 30000 00000000 80000000 00040000 00020010
# CHECK-NEXT: 30000 00000000 80000000 00040000 00000000
# ^ %hi(loc)
# ^ %got(bar)
# CHECK-NEXT: 30010 00020000 00040000
# ^ %got_hi/lo(start)
# ^ %got_hi/lo(loc)
# ^ redundant entry
# CHECK-NEXT: 30010 00020010 00020000 00040000
# ^ %got(bar)
# ^ %got_hi/lo(start)
# ^ %got_hi/lo(loc)
# CHECK: 00040000 .data 00000000 loc
# CHECK: 00020000 .text 00000000 __start