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1 # Introduction | 1 # Windows Split DLLs |
2 | 2 |
3 A build mode where chrome.dll is split into two separate DLLs. This was undertak
en as one possible workaround for toolchain limitations on Windows. | 3 A build mode where chrome.dll is split into two separate DLLs. This was |
4 | 4 undertaken as one possible workaround for toolchain limitations on Windows. |
5 | |
6 # Details | |
7 | 5 |
8 ## How | 6 ## How |
9 | 7 |
10 Normally, you probably don't need to worry about doing this build. If for some r
eason you need to build it locally: | 8 Normally, you probably don't need to worry about doing this build. If for some |
| 9 reason you need to build it locally: |
11 | 10 |
12 * From a _Visual Studio Command Prompt_ running as **Administrator** run `pyth
on tools\win\split_link\install_split_link.py`. | 11 1. From a _Visual Studio Command Prompt_ running as **Administrator** run |
13 * Set `GYP_DEFINES=chrome_split_dll=1`. In particular, don't have `component=s
hared_library`. Other things, like `buildtype` or `fastbuild` are fine. | 12 `python tools\win\split_link\install_split_link.py`. |
14 * `gclient runhooks` | 13 1. Set `GYP_DEFINES=chrome_split_dll=1`. In particular, don't have |
15 * `ninja -C out\Release chrome` | 14 `component=shared_library`. Other things, like `buildtype` or `fastbuild` |
| 15 are fine. |
| 16 1. `gclient runhooks` |
| 17 1. `ninja -C out\Release chrome` |
16 | 18 |
17 `chrome_split_dll` currently applies only to chrome.dll (and not test binaries). | 19 `chrome_split_dll` currently applies only to chrome.dll (and not test binaries). |
18 | 20 |
19 ## What | 21 ## What |
20 | 22 |
21 This is intended to be a temporary measure until either the toolchain is improve
d or the code can be physically separated into two DLLs (based on a browser/chil
d split). | 23 This is intended to be a temporary measure until either the toolchain is |
| 24 improved or the code can be physically separated into two DLLs (based on a |
| 25 browser/child split). |
22 | 26 |
23 The link replacement forcibly splits chrome.dll into two halves based on a descr
iption in `build\split_link_partition.py`. Code is primarily split along browser
/renderer lines. Roughly, Blink and its direct dependencies are in the "chrome1.
dll", and the rest of the browser code remains in "chrome.dll". | 27 The link replacement forcibly splits chrome.dll into two halves based on a |
| 28 description in `build\split_link_partition.py`. Code is primarily split along |
| 29 browser/renderer lines. Roughly, Blink and its direct dependencies are in the |
| 30 "chrome1.dll", and the rest of the browser code remains in "chrome.dll". |
24 | 31 |
25 Splitting the code this way allows keeping maximum optimization on the Blink por
tion of the code, which is important for performance. | 32 TODO: build\split_link_partition.py doesn't exist. |
26 | 33 |
27 There is a compile time define set when building in this mode `CHROME_SPLIT_DLL`
, however it should be used very sparingly-to-not-at-all. | 34 Splitting the code this way allows keeping maximum optimization on the Blink |
| 35 portion of the code, which is important for performance. |
| 36 |
| 37 There is a compile time define set when building in this mode |
| 38 `CHROME_SPLIT_DLL`, however it should be used very sparingly-to-not-at-all. |
28 | 39 |
29 ## Details | 40 ## Details |
30 | 41 |
31 This forcible split is implemented by putting .lib files in either one DLL or th
e other, and causing unresolved externals that result during linking to be forci
bly exported from the other DLL. This works relatively cleanly for function impo
rt/export, however it cannot work for data export. | 42 This forcible split is implemented by putting .lib files in either one DLL or |
| 43 the other, and causing unresolved externals that result during linking to be |
| 44 forcibly exported from the other DLL. This works relatively cleanly for function |
| 45 import/export, however it cannot work for data export. |
32 | 46 |
33 There are relatively few instances where data exports are required across the DL
L boundary. The waterfall builder http://build.chromium.org/p/chromium/waterfall
?show=Win%20Split will detect when new data exports are added, and these will ne
ed to be repaired. For constants, the data can be duplicated to both DLLs, but f
or writeable data, a wrapping set/get function will need to be added. | 47 There are relatively few instances where data exports are required across the |
| 48 DLL boundary. The waterfall builder |
| 49 http://build.chromium.org/p/chromium/waterfall?show=Win%20Split will detect when |
| 50 new data exports are added, and these will need to be repaired. For constants, |
| 51 the data can be duplicated to both DLLs, but for writeable data, a wrapping |
| 52 set/get function will need to be added. |
34 | 53 |
35 Some more details can be found on the initial commit of the split\_link script h
ttp://src.chromium.org/viewvc/chrome?revision=200049&view=revision and the assoc
iated bugs: http://crbug.com/237249 http://crbug.com/237267 | 54 http://build.chromium.org/p/chromium/waterfall?show=Win%20Split does not exist. |
| 55 |
| 56 Some more details can be found on the initial commit of the split_link script |
| 57 http://src.chromium.org/viewvc/chrome?revision=200049&view=revision and the |
| 58 associated bugs: http://crbug.com/237249 http://crbug.com/237267. |
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