Request for review: support building hotspot with gcc 4.6

[David Holmes]

Erik Trimble said the following on 04/30/11 10:27:
> On 4/29/2011 5:17 PM, David Holmes wrote:
>> David Katleman said the following on 04/30/11 09:13:
>>> On 4/29/2011 3:59 PM, Omair Majid wrote:
>>>>
>>>> http://cr.openjdk.java.net/~omajid/webrevs/gcc-46-support/
>>>>
>>>> The patch adds support for building hotspot with gcc 4.6. gcc 4.6 
>>>> changed how arguments are handled. It now treats -export-dynamic as 
>>>> it treats any other -efoo option: it thinks xport-dynamic is the 
>>>> entry point and passes this information to the linker. Since 
>>>> -export-dynamic is not passed to the linker, not all symbols will be 
>>>> exported by the linker. The bfd-based linker, given the invalid 
>>>> entry point xport-dynamic, simply ignores it. The gold linker, 
>>>> however, crashes causing the build to fail.
>>>>
>>>> Since -export-dynamic is a linker option, the correct way to pass it 
>>>> is using -Wl,-export-dynamic (or -Xlinker -export-dynamic). We have 
>>>> had this patch in IcedTea6 for a while now, but it would be nice if 
>>>> this was in OpenJDK too.
>>>
>>> Seems like your change should be surrounded by an ifneq that enables 
>>> your change for 4.6 and later
>>
>> Changing the use of a linker option:
>>
>>  -foo
>>
>> to
>>
>> -Xlinker -foo  (or -Wl,-foo)
>>
>> is fully compatible and preferable. We've been making a number of such 
>> changes ourselves (-Xlinker form) because they are needed when working 
>> with some of the cross-compilers we use for embedded.
>>
>> David Holmes
>> ------------
>>
>>> Example elsewhere in the file
>>>
>>>>   129 # Except for a few acceptable ones
>>>>   130 # Since GCC 4.3, -Wconversion has changed its meanings to warn 
>>>> these implicit
>>>>   131 # conversions which might affect the values. To avoid that, we 
>>>> need to turn
>>>>   132 # it off explicitly.
>>>>   133 ifneq "$(shell expr \( $(CC_VER_MAJOR) \>  4 \) \| \( \( 
>>>> $(CC_VER_MAJOR) = 4 \) \&  \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
>>>>   134 ACCEPTABLE_WARNINGS = -Wpointer-arith -Wsign-compare
>>>>   135 else
>>>>   136 ACCEPTABLE_WARNINGS = -Wpointer-arith -Wconversion -Wsign-compare
>>>>   137 endif
>>>
>>> Thanks
>>>         Dave
>>>
> 
> Presuming that the changes are still valid for a GCC and early libc in 
> the 3.x range (i.e. older 2.4-based releases), then it's OK to not use 
> ifneq
> 
> Otherwise, we should use ifneq to cover the versions of GCC/libc where 
> this is a valid option.
> 
> We (Oracle) and others still support older Linux distros, so we do need 
> to be careful not to break anything unless we specifically mean to (and, 
> have a good reason to cause such breakage).

As long as the gcc version recognizes -Xlinker (and/or -Wl,) then as I 
said changing from direct use of -foo to "-Xlinker -foo" is 100% compatible.

We already use -Xlinker and -Wl, all over the place! So this change 
should not have any compatibility issues whatsoever.

David
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