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src: start the .text section with an asm symbol #31981

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src: start the .text section with an asm symbol #31981

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00787b5
src: start the .text section with an asm symbol
Feb 27, 2020
174b6ba
Remove braces around single-statement if-body
Feb 28, 2020
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20 changes: 20 additions & 0 deletions node.gyp
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Expand Up @@ -313,6 +313,19 @@
},

'targets': [
{
'target_name': 'node_text_start',
'type': 'none',
'conditions': [
[ 'OS=="linux" and '
'target_arch=="x64"', {
'type': 'static_library',
'sources': [
'src/large_pages/node_text_start.S'
]
}],
]
},
{
'target_name': '<(node_core_target_name)',
'type': 'executable',
Expand Down Expand Up @@ -498,6 +511,13 @@
'src/node_snapshot_stub.cc'
],
}],
[ 'OS=="linux" and '
'target_arch=="x64"', {
'dependencies': [ 'node_text_start' ],
'ldflags+': [
'<(PRODUCT_DIR)/obj.target/node_text_start/src/large_pages/node_text_start.o'
]
}],
],
}, # node_core_target_name
{
Expand Down
29 changes: 15 additions & 14 deletions src/large_pages/node_large_page.cc
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Expand Up @@ -71,7 +71,11 @@

#if defined(__linux__)
extern "C" {
extern char __executable_start;
// This symbol must be declared weak because this file becomes part of all
// Node.js targets (like node_mksnapshot, node_mkcodecache, and cctest) and
// those files do not supply the symbol.
extern char __attribute__((weak)) __node_text_start;
extern char __start_lpstub;
} // extern "C"
#endif // defined(__linux__)

Expand Down Expand Up @@ -121,6 +125,8 @@ struct text_region FindNodeTextRegion() {
std::string dev;
char dash;
uintptr_t start, end, offset, inode;
uintptr_t node_text_start = reinterpret_cast<uintptr_t>(&__node_text_start);
uintptr_t lpstub_start = reinterpret_cast<uintptr_t>(&__start_lpstub);

ifs.open("/proc/self/maps");
if (!ifs) {
Expand All @@ -144,21 +150,16 @@ struct text_region FindNodeTextRegion() {
std::string pathname;
iss >> pathname;

if (start != reinterpret_cast<uintptr_t>(&__executable_start))
if (permission != "r-xp")
continue;

// The next line is our .text section.
if (!std::getline(ifs, map_line))
break;

iss = std::istringstream(map_line);
iss >> std::hex >> start;
iss >> dash;
iss >> std::hex >> end;
iss >> permission;
if (node_text_start < start || node_text_start >= end)
continue;

if (permission != "r-xp")
break;
start = node_text_start;
if (lpstub_start > start && lpstub_start <= end) {
end = lpstub_start;
}
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char* from = reinterpret_cast<char*>(hugepage_align_up(start));
char* to = reinterpret_cast<char*>(hugepage_align_down(end));
Expand Down Expand Up @@ -318,7 +319,7 @@ static bool IsSuperPagesEnabled() {
// d. If successful copy the code there and unmap the original region
int
#if !defined(__APPLE__)
__attribute__((__section__(".lpstub")))
__attribute__((__section__("lpstub")))
#else
__attribute__((__section__("__TEXT,__lpstub")))
#endif
Expand Down
5 changes: 5 additions & 0 deletions src/large_pages/node_text_start.S
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@@ -0,0 +1,5 @@
.text
.align 0x2000
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Why 8k?

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Good question, actually. I'm not sure we need it, because we end up snipping the front and the back off the .text if it doesn't align at 2MiB anyway, leaving the snipped-off bits on 4KiB pages.

.global __node_text_start
.hidden __node_text_start
__node_text_start: