commit d00febdab0535546ccbf1ef634be1f23b09c8b77
author Nikhil Benesch <nikhil.benesch@gmail.com> Sun Oct 04 02:03:36 2020 -0400
committer Ian Lance Taylor <iant@golang.org> Tue Oct 06 00:36:42 2020 +0000
tree 27ea6a5ca4a8aa5f920486dcbbc9b6f079a3795d
parent 801c458a562d22260ff176c26d65639dd32c8a90

gofrontend: correct file reading logic in Stream_from_file

The implementation of Stream_from_file mishandled several cases:

  * It reversed the check for whether bytes were already available in
    the peek buffer.

  * It considered positive return values from lseek to be an error, when
    only a -1 return value indicates an error.

Change-Id: Ic699d3ff7fe589f5ca2362b3db2971a6b9dc9022
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/259437
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Cherry Zhang <cherryyz@google.com>

go/import.cc

diff --git a/go/import.cc b/go/import.cc
index c63ae24..081afef 100644
--- a/go/import.cc
+++ b/go/import.cc
@@ -1487,7 +1487,7 @@
 bool
 Stream_from_file::do_peek(size_t length, const char** bytes)
 {
-  if (this->data_.length() <= length)
+  if (this->data_.length() >= length)
     {
       *bytes = this->data_.data();
       return true;
@@ -1504,7 +1504,7 @@
       return false;
     }
 
-  if (lseek(this->fd_, - got, SEEK_CUR) != 0)
+  if (lseek(this->fd_, - got, SEEK_CUR) < 0)
     {
       if (!this->saw_error())
 	go_fatal_error(Linemap::unknown_location(), "lseek failed: %m");
@@ -1524,7 +1524,7 @@
 void
 Stream_from_file::do_advance(size_t skip)
 {
-  if (lseek(this->fd_, skip, SEEK_CUR) != 0)
+  if (lseek(this->fd_, skip, SEEK_CUR) < 0)
     {
       if (!this->saw_error())
 	go_fatal_error(Linemap::unknown_location(), "lseek failed: %m");
@@ -1532,7 +1532,7 @@
     }
   if (!this->data_.empty())
     {
-      if (this->data_.length() < skip)
+      if (this->data_.length() > skip)
 	this->data_.erase(0, skip);
       else
 	this->data_.clear();