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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - lld-created binaries do not end up in disk cache (?)"
href="https://bugs.llvm.org/show_bug.cgi?id=32718">32718</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>lld-created binaries do not end up in disk cache (?)
</td>
</tr>
<tr>
<th>Product</th>
<td>lld
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>ELF
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>richard-llvm@metafoo.co.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>After linking Clang with ld.bfd or ld.gold, if I run the binary, it starts
~instantly. If I instead link with ld.lld, I incur a several second startup
time the first time I run the Clang binary, and 'perf' indicates the time is
spent paging in the binary.
Here's what ld.bfd does to create its output binary (when the output file
already exists):
stat("x", {st_mode=S_IFREG|0750, st_size=1079, ...}) = 0
lstat("x", {st_mode=S_IFREG|0750, st_size=1079, ...}) = 0
unlink("x") = 0
open("x", O_RDWR|O_CREAT|O_TRUNC, 0666) = 3
fcntl(3, F_GETFD) = 0
fcntl(3, F_SETFD, FD_CLOEXEC) = 0
fstat(3, {st_mode=S_IFREG|0640, st_size=0, ...}) = 0
lseek(3, 0, SEEK_SET) = 0
read(3, "", 64) = 0
lseek(3, 64, SEEK_CUR) = 64
write(3, "\1\0\0\0\5\0\0\0\0\0\0\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0"...,
120) = 120
# ... lots more seeking, reading, and writing on fd 3
write(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
448) = 448
close(3) = 0
stat("x", {st_mode=S_IFREG|0640, st_size=1079, ...}) = 0
umask(0) = 027
umask(027) = 0
chmod("x", 0750) = 0
Here's what ld.gold does:
stat("x", {st_mode=S_IFREG|0750, st_size=1079, ...}) = 0
unlink("x") = 0
open("x", O_RDWR|O_CREAT|O_TRUNC|O_CLOEXEC, 0777) = 4
fstat(4, {st_mode=S_IFREG|0750, st_size=0, ...}) = 0
fallocate(4, 0, 0, 1072) = 0
mmap(NULL, 1072, PROT_READ|PROT_WRITE, MAP_SHARED, 4, 0) = 0x7fdfec2db000
munmap(0x7fdfec2db000, 1072) = 0
close(4) = 0
Here's what ld.lld does:
access("x", F_OK) = 0
access("xtmp5181559f", F_OK) = -1 ENOENT (No such file or directory)
rename("x", "xtmp5181559f") = 0
stat("x", 0x7ffd9649e180) = -1 ENOENT (No such file or directory)
lstat("x", 0x7ffd9649e220) = -1 ENOENT (No such file or directory)
open("x.tmp3566de2", O_RDWR|O_CREAT|O_EXCL|O_TRUNC|O_CLOEXEC, 0777) = 3
fallocate(3, 0, 0, 4736) = 0
mmap(NULL, 4736, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0x7fd09a5bf000
close(3) = 0
munmap(0x7fd09a5bf000, 4736) = 0
rename("x.tmp3566de2", "x") = 0
There are a few odd things here. Using temporary files (which sometimes get
left behind!) seems unnecessary and error-prone, and stat'ing a file we just
renamed seems pointless. But I suspect the slowness is caused either by the
rename or by the relative order of the close and munmap calls.</pre>
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