[Lldb-commits] [lldb] r259611 - The compiler may use "line number 0" to indicate compiler generated goo that it can't
Zachary Turner via lldb-commits
lldb-commits at lists.llvm.org
Wed Feb 3 12:54:46 PST 2016
I asked around a little bit, and it seems like you do this by hand-writing
some LLVM IR (limiting yourself to a subset that is sufficiently platform
independent) and having clang link that in alongside a regular executable.
Then call your LLVM IR function from C++ and step over it. Would that work?
You'd probably need to talk to one of the LLVM guys to figure out how to do
that, but it seems like it should work.
Assuming it does, this technique would also open the door to writing a lot
of test cases that have historically been very difficult to write (such as
unwinder tests that need frames to be constructed a specific way, etc).
On Tue, Feb 2, 2016 at 5:31 PM Jim Ingham <jingham at apple.com> wrote:
> I don't think Clang does this right now, but Adrian says they are
> considering doing it to solve some problems they have with keeping track of
> nested inlines.
>
> Swift does it, but the compiler makes no guarantees as to when this will
> happen. It isn't controlled by some pragma, builtin or whatever. So I
> know some places where it will happen today, but there's no guarantee it
> will continue to happen in the future. So I'll have to write a test that
> works with the current compiler, and fails if the compiler changes so the
> relevant function no longer has line number 0 code right after the
> prologue. Yuck!
>
> I don't think it will be any different with clang when/if it starts doing
> this.
>
> Jim
>
>
> > On Feb 2, 2016, at 4:14 PM, Zachary Turner <zturner at google.com> wrote:
> >
> > Shouldn't it be possible to force clang to generate code like this? If
> so couldn't you write a test for this by stepping over a function call
> which has this kind of code in it?
> >
> > On Tue, Feb 2, 2016 at 4:11 PM Jim Ingham via lldb-commits <
> lldb-commits at lists.llvm.org> wrote:
> > Author: jingham
> > Date: Tue Feb 2 18:07:23 2016
> > New Revision: 259611
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=259611&view=rev
> > Log:
> > The compiler may use "line number 0" to indicate compiler generated goo
> that it can't
> > track a source for. When we are pushing breakpoints and stepping past
> function prologues,
> > also push past code from line 0 immediately following the prologue end.
> >
> > <rdar://problem/23730696>
> >
> > Modified:
> > lldb/trunk/include/lldb/Symbol/Function.h
> > lldb/trunk/source/Symbol/Function.cpp
> >
> > Modified: lldb/trunk/include/lldb/Symbol/Function.h
> > URL:
> http://llvm.org/viewvc/llvm-project/lldb/trunk/include/lldb/Symbol/Function.h?rev=259611&r1=259610&r2=259611&view=diff
> >
> ==============================================================================
> > --- lldb/trunk/include/lldb/Symbol/Function.h (original)
> > +++ lldb/trunk/include/lldb/Symbol/Function.h Tue Feb 2 18:07:23 2016
> > @@ -574,6 +574,14 @@ public:
> > CompilerType
> > GetCompilerType ();
> >
> > + //------------------------------------------------------------------
> > + /// Get the size of the prologue instructions for this function.
> The "prologue"
> > + /// instructions include any instructions given line number 0
> immediately following
> > + /// the prologue end.
> > + ///
> > + /// @return
> > + /// The size of the prologue.
> > + //------------------------------------------------------------------
> > uint32_t
> > GetPrologueByteSize ();
> >
> >
> > Modified: lldb/trunk/source/Symbol/Function.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Symbol/Function.cpp?rev=259611&r1=259610&r2=259611&view=diff
> >
> ==============================================================================
> > --- lldb/trunk/source/Symbol/Function.cpp (original)
> > +++ lldb/trunk/source/Symbol/Function.cpp Tue Feb 2 18:07:23 2016
> > @@ -570,6 +570,8 @@ Function::GetPrologueByteSize ()
> > {
> > m_flags.Set(flagsCalculatedPrologueSize);
> > LineTable* line_table = m_comp_unit->GetLineTable ();
> > + uint32_t prologue_end_line_idx = 0;
> > +
> > if (line_table)
> > {
> > LineEntry first_line_entry;
> > @@ -578,9 +580,12 @@ Function::GetPrologueByteSize ()
> > {
> > // Make sure the first line entry isn't already the end
> of the prologue
> > addr_t prologue_end_file_addr = LLDB_INVALID_ADDRESS;
> > + addr_t line_zero_end_file_addr = LLDB_INVALID_ADDRESS;
> > +
> > if (first_line_entry.is_prologue_end)
> > {
> > prologue_end_file_addr =
> first_line_entry.range.GetBaseAddress().GetFileAddress();
> > + prologue_end_line_idx = first_line_entry_idx;
> > }
> > else
> > {
> > @@ -595,6 +600,7 @@ Function::GetPrologueByteSize ()
> > if (line_entry.is_prologue_end)
> > {
> > prologue_end_file_addr =
> line_entry.range.GetBaseAddress().GetFileAddress();
> > + prologue_end_line_idx = idx;
> > break;
> > }
> > }
> > @@ -607,7 +613,7 @@ Function::GetPrologueByteSize ()
> > {
> > // Check the first few instructions and look for
> one that has
> > // a line number that's different than the first
> entry.
> > - const uint32_t last_line_entry_idx =
> first_line_entry_idx + 6;
> > + uint32_t last_line_entry_idx = first_line_entry_idx
> + 6;
> > for (uint32_t idx = first_line_entry_idx + 1; idx <
> last_line_entry_idx; ++idx)
> > {
> > LineEntry line_entry;
> > @@ -616,6 +622,7 @@ Function::GetPrologueByteSize ()
> > if (line_entry.line !=
> first_line_entry.line)
> > {
> > prologue_end_file_addr =
> line_entry.range.GetBaseAddress().GetFileAddress();
> > + prologue_end_line_idx = idx;
> > break;
> > }
> > }
> > @@ -624,10 +631,37 @@ Function::GetPrologueByteSize ()
> > if (prologue_end_file_addr == LLDB_INVALID_ADDRESS)
> > {
> > prologue_end_file_addr =
> first_line_entry.range.GetBaseAddress().GetFileAddress() +
> first_line_entry.range.GetByteSize();
> > + prologue_end_line_idx = first_line_entry_idx;
> > }
> > }
> > +
> > const addr_t func_start_file_addr =
> m_range.GetBaseAddress().GetFileAddress();
> > const addr_t func_end_file_addr = func_start_file_addr
> + m_range.GetByteSize();
> > +
> > + // Now calculate the offset to pass the subsequent line
> 0 entries.
> > + uint32_t first_non_zero_line = prologue_end_line_idx;
> > + while (1)
> > + {
> > + LineEntry line_entry;
> > + if
> (line_table->GetLineEntryAtIndex(first_non_zero_line, line_entry))
> > + {
> > + if (line_entry.line != 0)
> > + break;
> > + }
> > + if
> (line_entry.range.GetBaseAddress().GetFileAddress() >= func_end_file_addr)
> > + break;
> > +
> > + first_non_zero_line++;
> > + }
> > +
> > + if (first_non_zero_line > prologue_end_line_idx)
> > + {
> > + LineEntry first_non_zero_entry;
> > + if
> (line_table->GetLineEntryAtIndex(first_non_zero_line, first_non_zero_entry))
> > + {
> > + line_zero_end_file_addr =
> first_non_zero_entry.range.GetBaseAddress().GetFileAddress();
> > + }
> > + }
> >
> > // Verify that this prologue end file address in the
> function's
> > // address range just to be sure
> > @@ -635,10 +669,16 @@ Function::GetPrologueByteSize ()
> > {
> > m_prologue_byte_size = prologue_end_file_addr -
> func_start_file_addr;
> > }
> > +
> > + if (prologue_end_file_addr < line_zero_end_file_addr &&
> line_zero_end_file_addr < func_end_file_addr)
> > + {
> > + m_prologue_byte_size += line_zero_end_file_addr -
> prologue_end_file_addr;
> > + }
> > }
> > }
> > }
> > - return m_prologue_byte_size;
> > +
> > + return m_prologue_byte_size;
> > }
> >
> > lldb::LanguageType
> >
> >
> > _______________________________________________
> > lldb-commits mailing list
> > lldb-commits at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
>
>
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