From ebaa4deaf9f3bec32443e60fe74fce14686b4706 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Wed, 4 Jul 2018 03:01:33 +0000 Subject: [PATCH] i386: Add indirect_return function attribute On x86, swapcontext may return via indirect branch when shadow stack is enabled. To support code instrumentation of control-flow transfers with -fcf-protection, add indirect_return function attribute to inform compiler that a function may return via indirect branch. Note: Unlike setjmp, swapcontext only returns once. Mark it return twice will unnecessarily disable compiler optimization as shown in the testcase here. gcc/ PR target/85620 * config/i386/i386.c (rest_of_insert_endbranch): Also generate ENDBRANCH for non-tail call which may return via indirect branch. * doc/extend.texi: Document indirect_return attribute. gcc/testsuite/ PR target/85620 * gcc.target/i386/pr85620-1.c: New test. * gcc.target/i386/pr85620-2.c: Likewise. * gcc.target/i386/pr85620-3.c: Likewise. * gcc.target/i386/pr85620-4.c: Likewise. From-SVN: r262370 --- gcc/ChangeLog | 7 +++++++ gcc/config/i386/i386.c | 23 ++++++++++++++++++++++- gcc/doc/extend.texi | 6 ++++++ gcc/testsuite/ChangeLog | 8 ++++++++ gcc/testsuite/gcc.target/i386/pr85620-1.c | 15 +++++++++++++++ gcc/testsuite/gcc.target/i386/pr85620-2.c | 13 +++++++++++++ gcc/testsuite/gcc.target/i386/pr85620-3.c | 18 ++++++++++++++++++ gcc/testsuite/gcc.target/i386/pr85620-4.c | 18 ++++++++++++++++++ 8 files changed, 107 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/gcc.target/i386/pr85620-1.c create mode 100644 gcc/testsuite/gcc.target/i386/pr85620-2.c create mode 100644 gcc/testsuite/gcc.target/i386/pr85620-3.c create mode 100644 gcc/testsuite/gcc.target/i386/pr85620-4.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index cd8f6ab5cbc..05d1e05e990 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,10 @@ +2018-07-03 H.J. Lu + + PR target/85620 + * config/i386/i386.c (rest_of_insert_endbranch): Also generate + ENDBRANCH for non-tail call which may return via indirect branch. + * doc/extend.texi: Document indirect_return attribute. + 2018-07-03 Martin Sebor PR tree-optimization/86274 diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c index e6d17632142..41461d582a4 100644 --- a/gcc/config/i386/i386.c +++ b/gcc/config/i386/i386.c @@ -2621,7 +2621,26 @@ rest_of_insert_endbranch (void) { if (CALL_P (insn)) { - if (find_reg_note (insn, REG_SETJMP, NULL) == NULL) + bool need_endbr; + need_endbr = find_reg_note (insn, REG_SETJMP, NULL) != NULL; + if (!need_endbr && !SIBLING_CALL_P (insn)) + { + rtx call = get_call_rtx_from (insn); + rtx fnaddr = XEXP (call, 0); + + /* Also generate ENDBRANCH for non-tail call which + may return via indirect branch. */ + if (MEM_P (fnaddr) + && GET_CODE (XEXP (fnaddr, 0)) == SYMBOL_REF) + { + tree fndecl = SYMBOL_REF_DECL (XEXP (fnaddr, 0)); + if (fndecl + && lookup_attribute ("indirect_return", + DECL_ATTRIBUTES (fndecl))) + need_endbr = true; + } + } + if (!need_endbr) continue; /* Generate ENDBRANCH after CALL, which can return more than twice, setjmp-like functions. */ @@ -45897,6 +45916,8 @@ static const struct attribute_spec ix86_attribute_table[] = ix86_handle_fndecl_attribute, NULL }, { "function_return", 1, 1, true, false, false, false, ix86_handle_fndecl_attribute, NULL }, + { "indirect_return", 0, 0, true, false, false, false, + ix86_handle_fndecl_attribute, NULL }, /* End element. */ { NULL, 0, 0, false, false, false, false, NULL, NULL } diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 19c2da2e5db..071d0ffc414 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -5886,6 +5886,12 @@ foo (void) @} @end smallexample +@item indirect_return +@cindex @code{indirect_return} function attribute, x86 + +The @code{indirect_return} attribute on a function is used to inform +the compiler that the function may return via indirect branch. + @end table On the x86, the inliner does not inline a diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 020bed84961..a0e6ec2d776 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,11 @@ +2018-07-03 H.J. Lu + + PR target/85620 + * gcc.target/i386/pr85620-1.c: New test. + * gcc.target/i386/pr85620-2.c: Likewise. + * gcc.target/i386/pr85620-3.c: Likewise. + * gcc.target/i386/pr85620-4.c: Likewise. + 2018-07-03 Martin Sebor PR tree-optimization/86274 diff --git a/gcc/testsuite/gcc.target/i386/pr85620-1.c b/gcc/testsuite/gcc.target/i386/pr85620-1.c new file mode 100644 index 00000000000..32efb08e59e --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr85620-1.c @@ -0,0 +1,15 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fcf-protection" } */ +/* { dg-final { scan-assembler-times {\mendbr} 2 } } */ + +struct ucontext; + +extern int bar (struct ucontext *) __attribute__((__indirect_return__)); + +extern int res; + +void +foo (struct ucontext *oucp) +{ + res = bar (oucp); +} diff --git a/gcc/testsuite/gcc.target/i386/pr85620-2.c b/gcc/testsuite/gcc.target/i386/pr85620-2.c new file mode 100644 index 00000000000..b2e680fa1fe --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr85620-2.c @@ -0,0 +1,13 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fcf-protection" } */ +/* { dg-final { scan-assembler-times {\mendbr} 1 } } */ + +struct ucontext; + +extern int bar (struct ucontext *) __attribute__((__indirect_return__)); + +int +foo (struct ucontext *oucp) +{ + return bar (oucp); +} diff --git a/gcc/testsuite/gcc.target/i386/pr85620-3.c b/gcc/testsuite/gcc.target/i386/pr85620-3.c new file mode 100644 index 00000000000..c70a5caf930 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr85620-3.c @@ -0,0 +1,18 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -Wno-attributes" } */ + +struct ucontext; + +extern int bar (struct ucontext *) __attribute__((__indirect_return__)); + +static int __attribute__ ((__always_inline__)) +foo (struct ucontext *oucp) +{ + return bar (oucp); +} + +int +test (struct ucontext *oucp) +{ + return foo (oucp); +} diff --git a/gcc/testsuite/gcc.target/i386/pr85620-4.c b/gcc/testsuite/gcc.target/i386/pr85620-4.c new file mode 100644 index 00000000000..13056c46e49 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr85620-4.c @@ -0,0 +1,18 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -Wno-attributes" } */ + +struct ucontext; + +extern int bar (struct ucontext *) __attribute__((__returns_twice__)); + +static int __attribute__ ((__always_inline__)) +foo (struct ucontext *oucp) /* { dg-error "setjmp" } */ +{ + return bar (oucp); +} + +int +test (struct ucontext *oucp) +{ + return foo (oucp); +} -- 2.30.2