Ignore NaCl st_blksize of 0 and buffer writes to raw_fd_ostream.

The default LLVM raw_fd_ostream buffer size is based on stat'ing the FD and then checking st_blksize. Unfortunately, in the NaCl sandboxed build of pnacl-sz, NaCl's syscall returns st_blksize of 0 which makes the writes unbuffered. There is a comment in "src/trusted/service_runtime/include/bits/stat.h": nacl_abi_blksize_t nacl_abi_st_blksize; /* not implemented */ And the " src/trusted/desc/" implementation sets this to 0. This results in half a million write syscalls to translate the GCC pexe, which roughly doubles the translation time in sandboxed mode vs unsandboxed mode. Manually set a buffer size (Linux st_blksize seems to be about 4KB for comparison). This drops the number of write syscalls to about 200 for translating the GCC pexe. BUG= https://code.google.com/p/nativeclient/issues/detail?id=4091 R=stichnot@chromium.org Review URL: https://codereview.chromium.org/969403003

Ignore NaCl st_blksize of 0 and buffer writes to raw_fd_ostream.
437ceff2 · Jan Voung · 5bc44313 · 437ceff2
Commit 437ceff2 authored Mar 03, 2015 by Jan Voung
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main.cpp src/main.cpp +3 -0

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--- a/src/main.cpp
+++ b/src/main.cpp
@@ -340,6 +340,9 @@ int main(int argc, char **argv) {
    std::error_code EC;
    raw_fd_ostream *FdOs =
        new raw_fd_ostream(OutputFilename, EC, sys::fs::F_None);
+    // NaCl sets st_blksize to 0, and LLVM uses that to pick the
+    // default preferred buffer size. Set to something non-zero.
+    FdOs->SetBufferSize(1 << 14);
    Os.reset(FdOs);
    if (EC) {
      *Ls << "Failed to open output file: " << OutputFilename << ":\n"