Re: [Patch] SourceLevelDebugPkg/SecPeiDebugAgentLib: Fix duplicate symbol

[Laszlo Ersek <lersek@redhat.com>]

CC Ard

On 05/24/17 02:27, Kinney, Michael D wrote:
> Andrew,
>
> I agree in this specific case, making the global variable static
> should also resolve this issue.
>
> In general, we do not make module global variables static, so the
> module global can be shared across multiple source files in the
> module implementation.

I think the default should be the reverse: give objects with static
storage duration ("global variables") internal linkage ("STATIC") by
default, and turn the linkage into external only if multiple source
files of the same module actually use the same object together. (In this
case the object will have to be declared in a module-internal header
file anyway.)

I grepped the tree for "mMemoryDiscoveredNotifyList", and there are more
instances, all exhibiting the same issue:

(1) MdeModulePkg/Core/DxeIplPeim/DxeLoad.c
(2) QuarkPlatformPkg/Platform/Pei/PlatformInit/PlatformEarlyInit.c
(3) SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c
(4) Vlv2TbltDevicePkg/PlatformPei/Platform.c

In each of these source files, the "mMemoryDiscoveredNotifyList"
variable
- has an initializer,
- is declared in file scope,
- has external linkage,
- has static storage duration,

thus the declaration qualifies as an "external definition" (of which
there may be at most one, for any given object, in the final linking).

In each of the four modules listed above, the
"mMemoryDiscoveredNotifyList" variable is only used in the same source
file that declares / defines the variable. Thus, the variable should be
made "STATIC" in every one of them.

> Not sure why this issue has not been seen with other tool chains.

I think it is either a gcc or a BaseTools (toolchain config) bug.

Namely, we faced a similar issue before: please refer to commit
214a3b79417f ("BaseTools GCC: avoid the use of COMMON symbols",
2015-12-08). In that commit, we made sure that gcc wouldn't silently
merge multiple external definitions (because that violated ISO C and
caused actual runtime bugs). As a result, uninitialized globals were no
longer placed in the COMMON section, but in the data section, and
multiple external definitions triggered a link editing error.

However, in this case we have initialized global variables, which are
*already* placed in the data section. I just built OVMF with
SOURCE_DEBUG_ENABLE, and verified the following:

(a)

> $ nm Build/OvmfX64/DEBUG_GCC48/X64/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib/OUTPUT/SecPeiDebugAgentLib.lib \
>   | grep mMemoryDiscoveredNotifyList
> 0000000000000000 D mMemoryDiscoveredNotifyList
>
> $ nm Build/OvmfX64/DEBUG_GCC48/X64/MdeModulePkg/Core/DxeIplPeim/DxeIpl/OUTPUT/DxeIpl.lib \
>   | grep mMemoryDiscoveredNotifyList
> 0000000000000000 D mMemoryDiscoveredNotifyList

The "D" mark means:
- "D" / "d": The symbol is in the initialized data section.
- uppercase: the symbol is global (external)

In other words, linking these two object archives together should fail.

(b)

> $ egrep 'SecPeiDebugAgentLib\.lib|DxeIpl\.lib' \
>   Build/OvmfX64/DEBUG_GCC48/X64/MdeModulePkg/Core/DxeIplPeim/DxeIpl/OUTPUT/static_library_files.lst
> .../Build/OvmfX64/DEBUG_GCC48/X64/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgentLib/OUTPUT/SecPeiDebugAgentLib.lib
> .../Build/OvmfX64/DEBUG_GCC48/X64/MdeModulePkg/Core/DxeIplPeim/DxeIpl/OUTPUT/DxeIpl.lib

This means that the build process will link them together. Indeed I can
find the following *successful* command in the build log (see the
reference to the above "static_library_files.lst" object list file):

> "gcc" \
>   -o \
>   Build/OvmfX64/DEBUG_GCC48/X64/MdeModulePkg/Core/DxeIplPeim/DxeIpl/DEBUG/DxeIpl.dll \
>   -nostdlib \
>   -Wl,-n,-q,--gc-sections \
>   -z common-page-size=0x20 \
>   -Wl,--entry,_ModuleEntryPoint \
>   -u _ModuleEntryPoint \
>   -Wl,-Map,Build/OvmfX64/DEBUG_GCC48/X64/MdeModulePkg/Core/DxeIplPeim/DxeIpl/DEBUG/DxeIpl.map \
>   -Wl,-melf_x86_64,--oformat=elf64-x86-64 \
>   -Wl,--start-group,@Build/OvmfX64/DEBUG_GCC48/X64/MdeModulePkg/Core/DxeIplPeim/DxeIpl/OUTPUT/static_library_files.lst,--end-group \
>   -g \
>   -fshort-wchar \
>   -fno-builtin \
>   -fno-strict-aliasing \
>   -Wall \
>   -Werror \
>   -Wno-array-bounds \
>   -ffunction-sections \
>   -fdata-sections \
>   -include AutoGen.h \
>   -fno-common \
>   -DSTRING_ARRAY_NAME=DxeIplStrings \
>   -m64 \
>   -fno-stack-protector \
>   "-DEFIAPI=__attribute__((ms_abi))" \
>   -maccumulate-outgoing-args \
>   -mno-red-zone \
>   -Wno-address \
>   -mcmodel=small \
>   -fpie \
>   -fno-asynchronous-unwind-tables \
>   -Wno-address \
>   -Os \
>   -mno-mmx \
>   -mno-sse \
>   -D DISABLE_NEW_DEPRECATED_INTERFACES \
>   -Wl,--defsym=PECOFF_HEADER_SIZE=0x228 \
>   -Wl,--script=BaseTools/Scripts/GccBase.lds

(c) Re-running the command manually succeeds.

(d) Just to see if "-fdata-sections" made any difference ("Place each
data item into its own section in the output file"), I removed it. Even
that way, the command succeeded.

I think this is either a gcc / GNU linker bug, or else our command line
(or linker script, "GccBase.lds") is buggy. This link command should not
succeed.

Anyway, regarding the patch, I think that all four declarations of
"mMemoryDiscoveredNotifyList" should be made STATIC instead.

Thanks,
Laszlo

>> -----Original Message-----
>> From: afish@apple.com [mailto:afish@apple.com]
>> Sent: Tuesday, May 23, 2017 4:26 PM
>> To: Kinney, Michael D <michael.d.kinney@intel.com>
>> Cc: edk2-devel@lists.01.org; Fan, Jeff <jeff.fan@intel.com>; Wu, Hao A
>> <hao.a.wu@intel.com>; Laszlo Ersek <lersek@redhat.com>
>> Subject: Re: [Patch] SourceLevelDebugPkg/SecPeiDebugAgentLib: Fix duplicate symbol
>>
>> Mike,
>>
>> Do the other compilers promote (or is that demote) to static? Would not making these
>> lib globals, and private functions static solve this class of issue?
>>
>> Thanks,
>>
>> Andrew Fish
>>
>>> On May 23, 2017, at 4:21 PM, Michael Kinney <michael.d.kinney@intel.com> wrote:
>>>
>>> https://bugzilla.tianocore.org/show_bug.cgi?id=573
>>>
>>> The SecPeiDebugAgentLib uses the global variable
>>> mMemoryDiscoveredNotifyList for a PPI notification on
>>> the Memory Discovered PPI.  This same variable name is
>>> used in the DxeIplPeim for the same PPI notification.
>>>
>>> The XCODE5 tool chain detects this duplicate symbol
>>> when the OVMF platform is built with the flag
>>> -D SOURCE_DEBUG_ENABLE.
>>>
>>> The fix is to rename this global variable in the
>>> SecPeiDebugAgentLib library.
>>>
>>> Cc: Andrew Fish <afish@apple.com>
>>> Cc: Jeff Fan <jeff.fan@intel.com>
>>> Cc: Hao Wu <hao.a.wu@intel.com>
>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>> Contributed-under: TianoCore Contribution Agreement 1.0
>>> Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
>>> ---
>>> .../Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c         | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git
>> a/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c
>> b/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c
>>> index b717e33..9f5223a 100644
>>> --- a/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c
>>> +++ b/SourceLevelDebugPkg/Library/DebugAgent/SecPeiDebugAgent/SecPeiDebugAgentLib.c
>>> @@ -32,7 +32,7 @@ GLOBAL_REMOVE_IF_UNREFERENCED EFI_PEI_PPI_DESCRIPTOR
>> mVectorHandoffInf
>>>   }
>>> };
>>>
>>> -GLOBAL_REMOVE_IF_UNREFERENCED EFI_PEI_NOTIFY_DESCRIPTOR
>> mMemoryDiscoveredNotifyList[1] = {
>>> +GLOBAL_REMOVE_IF_UNREFERENCED EFI_PEI_NOTIFY_DESCRIPTOR
>> mDebugAgentMemoryDiscoveredNotifyList[1] = {
>>>   {
>>>     (EFI_PEI_PPI_DESCRIPTOR_NOTIFY_CALLBACK |
>> EFI_PEI_PPI_DESCRIPTOR_TERMINATE_LIST),
>>>     &gEfiPeiMemoryDiscoveredPpiGuid,
>>> @@ -554,7 +554,7 @@ InitializeDebugAgent (
>>>     // Register for a callback once memory has been initialized.
>>>     // If memery has been ready, the callback funtion will be invoked immediately
>>>     //
>>> -    Status = PeiServicesNotifyPpi (&mMemoryDiscoveredNotifyList[0]);
>>> +    Status = PeiServicesNotifyPpi (&mDebugAgentMemoryDiscoveredNotifyList[0]);
>>>     if (EFI_ERROR (Status)) {
>>>       DEBUG ((EFI_D_ERROR, "DebugAgent: Failed to register memory discovered
>> callback function!\n"));
>>>       CpuDeadLoop ();
>>> --
>>> 2.6.3.windows.1
>>>
>