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Fix nested dereference rewrites #1835

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merged 2 commits into from
Jun 17, 2018
Merged

Fix nested dereference rewrites #1835

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3dabd3f
Fix nested rewrites dereferences
pchaigno Jun 17, 2018
0b4126c
Test for the rewrite of nested dereferences
pchaigno Jun 17, 2018
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Fix nested rewrites dereferences 
When the rewriter meets a dereference of a member dereference it
fails to properly rewrite them into calls to bpf_probe_read.  The
reason is that Clang is unable to track the position of rewritten
text, but we can accommodate this by inserting text around the
dereference instead of completely rewriting it.  We are already
doing that for member dereference, but not for simple dereference.
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@pchaigno
pchaigno committed Jun 17, 2018
commit 3dabd3f8226eea663ee3a3d525e39f98c9ac11c1
19 changes: 12 additions & 7 deletions src/cc/frontends/clang/b_frontend_action.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -388,12 +388,12 @@ bool ProbeVisitor::VisitUnaryOperator(UnaryOperator *E) {
if (!ProbeChecker(sub, ptregs_, track_helpers_).needs_probe())
return true;
memb_visited_.insert(E);
string rhs = rewriter_.getRewrittenText(expansionRange(sub->getSourceRange()));
string text;
text = "({ typeof(" + E->getType().getAsString() + ") _val; __builtin_memset(&_val, 0, sizeof(_val));";
text += " bpf_probe_read(&_val, sizeof(_val), (u64)";
text += rhs + "); _val; })";
rewriter_.ReplaceText(expansionRange(E->getSourceRange()), text);
string pre, post;
pre = "({ typeof(" + E->getType().getAsString() + ") _val; __builtin_memset(&_val, 0, sizeof(_val));";
pre += " bpf_probe_read(&_val, sizeof(_val), (u64)";
post = "); _val; })";
rewriter_.ReplaceText(expansionLoc(E->getOperatorLoc()), 1, pre);
rewriter_.InsertTextAfterToken(expansionLoc(sub->getLocEnd()), post);
return true;
}
bool ProbeVisitor::VisitMemberExpr(MemberExpr *E) {
Expand Down Expand Up @@ -442,7 +442,7 @@ bool ProbeVisitor::VisitMemberExpr(MemberExpr *E) {
pre = "({ typeof(" + E->getType().getAsString() + ") _val; __builtin_memset(&_val, 0, sizeof(_val));";
pre += " bpf_probe_read(&_val, sizeof(_val), (u64)&";
post = rhs + "); _val; })";
rewriter_.InsertText(E->getLocStart(), pre);
rewriter_.InsertText(expansionLoc(E->getLocStart()), pre);
rewriter_.ReplaceText(expansionRange(SourceRange(member, E->getLocEnd())), post);
return true;
}
Expand Down Expand Up @@ -495,6 +495,11 @@ ProbeVisitor::expansionRange(SourceRange range) {
#endif
}

SourceLocation
ProbeVisitor::expansionLoc(SourceLocation loc) {
return rewriter_.getSourceMgr().getExpansionLoc(loc);
}

template <unsigned N>
DiagnosticBuilder ProbeVisitor::error(SourceLocation loc, const char (&fmt)[N]) {
unsigned int diag_id = C.getDiagnostics().getCustomDiagID(DiagnosticsEngine::Error, fmt);
Expand Down
1 change: 1 addition & 0 deletions src/cc/frontends/clang/b_frontend_action.h
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Expand Up @@ -109,6 +109,7 @@ class ProbeVisitor : public clang::RecursiveASTVisitor<ProbeVisitor> {
bool assignsExtPtr(clang::Expr *E, int *nbAddrOf);
bool IsContextMemberExpr(clang::Expr *E);
clang::SourceRange expansionRange(clang::SourceRange range);
clang::SourceLocation expansionLoc(clang::SourceLocation loc);
template <unsigned N>
clang::DiagnosticBuilder error(clang::SourceLocation loc, const char (&fmt)[N]);

Expand Down